diff --git a/.github/workflows/ci-pipeline.yaml b/.github/workflows/ci-pipeline.yaml
index 2736c96..7b50c2a 100644
--- a/.github/workflows/ci-pipeline.yaml
+++ b/.github/workflows/ci-pipeline.yaml
@@ -12,6 +12,15 @@ on:
       - main
   pull_request:
   workflow_dispatch:
+    inputs:
+      grype_version:
+        description: "Grype version to install"
+        default: "v0.110.0"
+        type: string
+      grype_commit_sha:
+        description: "Grype commit SHA for install script"
+        default: "dee8de483dfba5b4e0bc0aa8e4ab2ce52137e490"
+        type: string
 
 jobs:
   build-verification:
@@ -27,7 +36,7 @@ jobs:
         with:
           terraform_version: 1.9.3
           terraform_wrapper: false
-        
+
       - name: Install Go
         uses: actions/setup-go@v6
         with:
@@ -97,17 +106,12 @@ jobs:
       - name: Run GitLeaks Scan
         run: gitleaks detect --source . --config .gitleaks.toml
 
-      - name: Install Trivy
+      - name: Install Grype
         run: |
-          sudo apt-get update
-          sudo apt-get install -y wget apt-transport-https gnupg lsb-release
-          wget -qO - https://aquasecurity.github.io/trivy-repo/deb/public.key | sudo apt-key add -
-          echo deb https://aquasecurity.github.io/trivy-repo/deb $(lsb_release -sc) main | sudo tee -a /etc/apt/sources.list.d/trivy.list
-          sudo apt-get update
-          sudo apt-get install -y trivy
+          curl -sSfL https://raw.githubusercontent.com/anchore/grype/${{ inputs.grype_commit_sha || 'dee8de483dfba5b4e0bc0aa8e4ab2ce52137e490' }}/install.sh | bash -s -- -b /usr/local/bin ${{ inputs.grype_version || 'v0.110.0' }}
 
-      - name: Run Trivy Scan
-        run: trivy filesystem --security-checks vuln,config --exit-code 1 --severity HIGH,CRITICAL --ignore-unfixed .
+      - name: Run Grype Filesystem Scan
+        run: grype "dir:./" --fail-on high
 
   publishing:
     name: Publish Release
@@ -118,7 +122,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
         with:
-          persist-credentials: false  # Disable default GITHUB_TOKEN persistence
+          persist-credentials: false # Disable default GITHUB_TOKEN persistence
 
       - name: Create Semantic Release
         uses: cycjimmy/semantic-release-action@v4.1.0
@@ -132,4 +136,4 @@ jobs:
           echo ${{ steps.semantic-release.outputs.new_release_version }}
           echo ${{ steps.semantic-release.outputs.new_release_major_version }}
           echo ${{ steps.semantic-release.outputs.new_release_minor_version }}
-          echo ${{ steps.semantic-release.outputs.new_release_patch_version }}
\ No newline at end of file
+          echo ${{ steps.semantic-release.outputs.new_release_patch_version }}
diff --git a/docs/usage.md b/docs/usage.md
index c05fad3..90bfdfe 100644
--- a/docs/usage.md
+++ b/docs/usage.md
@@ -79,7 +79,7 @@ module "my_backup" {
     backup2 = {
       backup_name                     = "storage2"
       retention_period                = "P30D"
-      backup_intervals                = ["R/2024-01-01T00:00:00+00:00/P2D"]
+      backup_intervals                = ["R/2024-01-01T00:00:00+00:00/P1W"]
       storage_account_id              = azurerm_storage_account.my_storage_account_2.id
       storage_account_containers      = ["container1", "container2"]
       backup_policy_naming_template   = "nhsuk-{resource_abbreviation}-{resource_type}-{backup_name}"
@@ -100,7 +100,7 @@ module "my_backup" {
     backup2 = {
       backup_name                     = "disk2"
       retention_period                = "P30D"
-      backup_intervals                = ["R/2024-01-01T00:00:00+00:00/P2D"]
+      backup_intervals                = ["R/2024-01-01T00:00:00+00:00/PT12H"]
       managed_disk_id                 = azurerm_managed_disk.my_managed_disk_2.id
       backup_policy_naming_template   = "nhsuk-{resource_abbreviation}-{resource_type}-{backup_name}"
       backup_instance_naming_template = "nhsuk-{resource_abbreviation}-{resource_type}-{backup_name}"
@@ -114,14 +114,14 @@ module "my_backup" {
     backup1 = {
       backup_name              = "server1"
       retention_period         = "P7D"
-      backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1D"]
+      backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1W"]
       server_id                = azurerm_postgresql_flexible_server.my_server_1.id
       server_resource_group_id = azurerm_resource_group.my_resource_group.id
     }
     backup2 = {
       backup_name                     = "server2"
       retention_period                = "P30D"
-      backup_intervals                = ["R/2024-01-01T00:00:00+00:00/P2D"]
+      backup_intervals                = ["R/2024-01-01T00:00:00+00:00/P1W"]
       server_id                       = azurerm_postgresql_flexible_server.my_server_2.id
       server_resource_group_id        = azurerm_resource_group.my_resource_group.id
       backup_policy_naming_template   = "nhsuk-{resource_abbreviation}-{resource_type}-{backup_name}"
@@ -150,7 +150,7 @@ module "my_backup" {
 | `blob_storage_backups.storage_account_containers` | A list of containers in the storage account that should be backed up. | Yes | n/a |
 | `blob_storage_backups.backup_name` | The name of the backup, which must be unique across blob storage backups. | Yes | n/a |
 | `blob_storage_backups.retention_period` | How long the backed up data will be retained for, which should be in `ISO 8601` duration format. This must be specified in days, and can be up to 7 days unless `use_extended_retention` is on. [See the following link for more information about the format](https://en.wikipedia.org/wiki/ISO_8601#Durations). | Yes | n/a |
-| `blob_storage_backups.backup_intervals` | A list of intervals at which backups should be taken, which should be in `ISO 8601` duration format. [See the following link for the possible values](https://en.wikipedia.org/wiki/ISO_8601#Time_intervals). | Yes | n/a |
+| `blob_storage_backups.backup_intervals` | A list of intervals at which backups should be taken, in `ISO 8601` repeating interval format. The frequency (duration) part must be `P1D` (daily) or `P1W` (weekly). [See the Azure Blob backup documentation for supported schedules](https://learn.microsoft.com/en-us/azure/backup/blob-backup-configure-manage). | Yes | n/a |
 | `blob_storage_backups.backup_policy_naming_template` | Naming template used to construct the blob backup instance name. The following placeholders are supported and will be replaced by the module: `{resource_abbreviation}` → `bkpol`, `{resource_type}` → `blob`, `{backup_name}` → value of `blob_storage_backups.backup_name` | No | {resource_abbreviation}-{resource_type}-{backup_name} |
 | `blob_storage_backups.backup_instance_naming_template` | Naming template used to construct the blob backup instance name. The following placeholders are supported and will be replaced by the module: `{resource_abbreviation}` → `bkinst`, `{resource_type}` → `blob`, `{backup_name}` → value of `blob_storage_backups.backup_name` | No | {resource_abbreviation}-{resource_type}-{backup_name} |
 | `blob_storage_backups.time_zone` | The time zone to apply to the backup policy schedule (eg. Europe/London). If not specified, Azure’s default time zone behaviour is used. | No | n/a |
@@ -159,7 +159,7 @@ module "my_backup" {
 | `managed_disk_backups.managed_disk_id` | The id of the managed disk that should be backed up. | Yes | n/a |
 | `managed_disk_backups.backup_name` | The name of the backup, which must be unique across managed disk backups. | Yes | n/a |
 | `managed_disk_backups.retention_period` | How long the backed up data will be retained for, which should be in `ISO 8601` duration format. This must be specified in days, and can be up to 7 days unless `use_extended_retention` is on. [See the following link for more information about the format](https://en.wikipedia.org/wiki/ISO_8601#Durations). | Yes | n/a |
-| `managed_disk_backups.backup_intervals` | A list of intervals at which backups should be taken, which should be in `ISO 8601` duration format. [See the following link for the possible values](https://en.wikipedia.org/wiki/ISO_8601#Time_intervals). | Yes | n/a |
+| `managed_disk_backups.backup_intervals` | A list of intervals at which backups should be taken, in `ISO 8601` repeating interval format. The frequency (duration) part must be one of `PT1H`, `PT2H`, `PT4H`, `PT6H`, `PT8H`, `PT12H` (hourly) or `P1D` (daily). [See the Azure Disk backup support matrix for supported schedules](https://learn.microsoft.com/en-us/azure/backup/disk-backup-support-matrix). | Yes | n/a |
 | `managed_disk_backup.backup_policy_naming_template` | Naming template used to construct the disk backup instance name. The following placeholders are supported and will be replaced by the module: `{resource_abbreviation}` → `bkpol`, `{resource_type}` → `disk`, `{backup_name}` → value of `managed_disk_backup.backup_name` | No | {resource_abbreviation}-{resource_type}-{backup_name} |
 | `managed_disk_backup.backup_instance_naming_template` | Naming template used to construct the disk backup instance name. The following placeholders are supported and will be replaced by the module: `{resource_abbreviation}` → `bkinst`, `{resource_type}` → `disk`, `{backup_name}` → value of `managed_disk_backup.backup_name` | No | {resource_abbreviation}-{resource_type}-{backup_name} |
 | `postgresql_flexible_server_backups` | A map of postgresql flexible server backups that should be created. For each backup the following values should be provided: `backup_name`, `server_id`, `server_resource_group_id`, `retention_period` and `backup_intervals`. When no value is provided then no backups are created. | No | n/a |
@@ -167,6 +167,6 @@ module "my_backup" {
 | `postgresql_flexible_server_backups.server_id` | The id of the postgresql flexible server that should be backed up. | Yes | n/a |
 | `postgresql_flexible_server_backups.server_resource_group_id` | The id of the resource group which the postgresql flexible server resides in. | Yes | n/a |
 | `postgresql_flexible_server_backups.retention_period` | How long the backed up data will be retained for, which should be in `ISO 8601` duration format. This must be specified in days, and can be up to 7 days unless `use_extended_retention` is on. [See the following link for more information about the format](https://en.wikipedia.org/wiki/ISO_8601#Durations). | Yes | n/a |
-| `postgresql_flexible_server_backups.backup_intervals` | A list of intervals at which backups should be taken, which should be in `ISO 8601` duration format. [See the following link for the possible values](https://en.wikipedia.org/wiki/ISO_8601#Time_intervals). | Yes | n/a |
+| `postgresql_flexible_server_backups.backup_intervals` | A list of intervals at which backups should be taken, in `ISO 8601` repeating interval format. Only `P1W` (weekly) is supported. [See the Azure PostgreSQL Flexible Server backup support matrix for supported schedules](https://learn.microsoft.com/en-us/azure/backup/backup-azure-database-postgresql-flex-support-matrix). | Yes | n/a |
 | `postgresql_flexible_server_backup.backup_policy_naming_template` | Naming template used to construct the pgflex server backup instance name. The following placeholders are supported and will be replaced by the module: `{resource_abbreviation}` → `bkpol`, `{resource_type}` → `pgflex`, `{backup_name}` → value of `postgresql_flexible_server_backup.backup_name` | No | {resource_abbreviation}-{resource_type}-{backup_name} |
 | `postgresql_flexible_server_backup.backup_instance_naming_template` | Naming template used to construct the pgflex server backup instance name. The following placeholders are supported and will be replaced by the module: `{resource_abbreviation}` → `bkinst`, `{resource_type}` → `pgflex`, `{backup_name}` → value of `postgresql_flexible_server_backup.backup_name` | No | {resource_abbreviation}-{resource_type}-{backup_name} |
diff --git a/infrastructure/variables.tf b/infrastructure/variables.tf
index 1fbe598..89d8de0 100644
--- a/infrastructure/variables.tf
+++ b/infrastructure/variables.tf
@@ -1,6 +1,17 @@
 locals {
   # The valid backup retention period - up to 7 days, which can be bypassed when use_extended_retention is set to true
   valid_retention_periods = [for days in range(1, 8) : "P${days}D"]
+
+  # Valid backup interval frequencies per resource type
+  valid_blob_storage_intervals               = ["P1D", "P1W"]
+  valid_managed_disk_intervals               = ["PT1H", "PT2H", "PT4H", "PT6H", "PT8H", "PT12H", "P1D"]
+  valid_postgresql_flexible_server_intervals = ["P1W"]
+
+  # Repeating interval format: R/<RFC3339 timestamp>/<duration>
+  backup_interval_timestamp_pattern = "[0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{2}:[0-9]{2}:[0-9]{2}(Z|[+-][0-9]{2}:[0-9]{2})"
+  blob_storage_interval_pattern     = "^R/${local.backup_interval_timestamp_pattern}/(${join("|", local.valid_blob_storage_intervals)})$"
+  managed_disk_interval_pattern     = "^R/${local.backup_interval_timestamp_pattern}/(${join("|", local.valid_managed_disk_intervals)})$"
+  postgresql_interval_pattern       = "^R/${local.backup_interval_timestamp_pattern}/(${join("|", local.valid_postgresql_flexible_server_intervals)})$"
 }
 
 variable "resource_group_name" {
@@ -75,6 +86,15 @@ variable "blob_storage_backups" {
     error_message = "At least one backup interval must be provided."
   }
 
+  validation {
+    condition = alltrue([
+      for k, v in var.blob_storage_backups : alltrue([
+        for interval in v.backup_intervals : can(regex(local.blob_storage_interval_pattern, interval))
+      ])
+    ])
+    error_message = "Invalid backup interval for blob storage: allowed frequencies are P1D (daily) or P1W (weekly). See https://learn.microsoft.com/en-us/azure/backup/blob-backup-configure-manage for details."
+  }
+
   validation {
     condition     = alltrue([for k, v in var.blob_storage_backups : length(v.storage_account_containers) > 0])
     error_message = "At least one storage account container must be provided."
@@ -108,6 +128,15 @@ variable "managed_disk_backups" {
     error_message = "At least one backup interval must be provided."
   }
 
+  validation {
+    condition = alltrue([
+      for k, v in var.managed_disk_backups : alltrue([
+        for interval in v.backup_intervals : can(regex(local.managed_disk_interval_pattern, interval))
+      ])
+    ])
+    error_message = "Invalid backup interval for managed disk: allowed frequencies are PT1H, PT2H, PT4H, PT6H, PT8H, PT12H (hourly) or P1D (daily). See https://learn.microsoft.com/en-us/azure/backup/disk-backup-support-matrix for details."
+  }
+
   validation {
     condition     = var.use_extended_retention ? true : alltrue([for k, v in var.managed_disk_backups : contains(local.valid_retention_periods, v.retention_period)])
     error_message = "Invalid retention period: valid periods are up to 7 days. If you require a longer retention period then please set use_extended_retention to true."
@@ -133,6 +162,15 @@ variable "postgresql_flexible_server_backups" {
     error_message = "At least one backup interval must be provided."
   }
 
+  validation {
+    condition = alltrue([
+      for k, v in var.postgresql_flexible_server_backups : alltrue([
+        for interval in v.backup_intervals : can(regex(local.postgresql_interval_pattern, interval))
+      ])
+    ])
+    error_message = "Invalid backup interval for PostgreSQL flexible server: only P1W (weekly) is allowed. See https://learn.microsoft.com/en-us/azure/backup/backup-azure-database-postgresql-flex-support-matrix for details."
+  }
+
   validation {
     condition     = var.use_extended_retention ? true : alltrue([for k, v in var.postgresql_flexible_server_backups : contains(local.valid_retention_periods, v.retention_period)])
     error_message = "Invalid retention period: valid periods are up to 7 days. If you require a longer retention period then please set use_extended_retention to true."
diff --git a/tests/end-to-end-tests/blob_storage_backup_test.go b/tests/end-to-end-tests/blob_storage_backup_test.go
index c56d657..7d523f0 100644
--- a/tests/end-to-end-tests/blob_storage_backup_test.go
+++ b/tests/end-to-end-tests/blob_storage_backup_test.go
@@ -77,7 +77,7 @@ func TestBlobStorageBackup(t *testing.T) {
 	blobStorageBackups := map[string]map[string]interface{}{
 		"backup1": {
 			"backup_name":                "blob1",
-			"retention_period":           "P1D",
+			"retention_period":           "P6D",
 			"backup_intervals":           []string{"R/2024-01-01T00:00:00+00:00/P1D"},
 			"storage_account_id":         *externalResources.StorageAccountOne.ID,
 			"storage_account_containers": []string{*externalResources.StorageAccountOneContainer.Name},
@@ -85,7 +85,7 @@ func TestBlobStorageBackup(t *testing.T) {
 		"backup2": {
 			"backup_name":                "blob2",
 			"retention_period":           "P7D",
-			"backup_intervals":           []string{"R/2024-01-01T00:00:00+00:00/P2D"},
+			"backup_intervals":           []string{"R/2024-01-01T00:00:00+00:00/P1W"},
 			"storage_account_id":         *externalResources.StorageAccountTwo.ID,
 			"storage_account_containers": []string{*externalResources.StorageAccountTwoContainer.Name},
 		},
diff --git a/tests/end-to-end-tests/managed_disk_backup_test.go b/tests/end-to-end-tests/managed_disk_backup_test.go
index 17bcf82..2d0a6aa 100644
--- a/tests/end-to-end-tests/managed_disk_backup_test.go
+++ b/tests/end-to-end-tests/managed_disk_backup_test.go
@@ -71,8 +71,8 @@ func TestManagedDiskBackup(t *testing.T) {
 	managedDiskBackups := map[string]map[string]interface{}{
 		"backup1": {
 			"backup_name":      "disk1",
-			"retention_period": "P1D",
-			"backup_intervals": []string{"R/2024-01-01T00:00:00+00:00/P1D"},
+			"retention_period": "P6D",
+			"backup_intervals": []string{"R/2024-01-01T00:00:00+00:00/PT6H"},
 			"managed_disk_id":  *externalResources.ManagedDiskOne.ID,
 			"managed_disk_resource_group": map[string]interface{}{
 				"id":   *externalResources.ResourceGroup.ID,
@@ -82,7 +82,7 @@ func TestManagedDiskBackup(t *testing.T) {
 		"backup2": {
 			"backup_name":      "disk2",
 			"retention_period": "P7D",
-			"backup_intervals": []string{"R/2024-01-01T00:00:00+00:00/P2D"},
+			"backup_intervals": []string{"R/2024-01-01T00:00:00+00:00/P1D"},
 			"managed_disk_id":  *externalResources.ManagedDiskTwo.ID,
 			"managed_disk_resource_group": map[string]interface{}{
 				"id":   *externalResources.ResourceGroup.ID,
diff --git a/tests/end-to-end-tests/postgresql_flexible_server_backup_test.go b/tests/end-to-end-tests/postgresql_flexible_server_backup_test.go
index d57c1a8..e9881ad 100644
--- a/tests/end-to-end-tests/postgresql_flexible_server_backup_test.go
+++ b/tests/end-to-end-tests/postgresql_flexible_server_backup_test.go
@@ -71,15 +71,15 @@ func TestPostgresqlFlexibleServerBackup(t *testing.T) {
 	PostgresqlFlexibleServerBackups := map[string]map[string]interface{}{
 		"backup1": {
 			"backup_name":              "server1",
-			"retention_period":         "P1D",
-			"backup_intervals":         []string{"R/2024-01-01T00:00:00+00:00/P1D"},
+			"retention_period":         "P6D",
+			"backup_intervals":         []string{"R/2024-01-01T00:00:00+00:00/P1W"},
 			"server_id":                *externalResources.PostgresqlFlexibleServerOne.ID,
 			"server_resource_group_id": *externalResources.ResourceGroup.ID,
 		},
 		"backup2": {
 			"backup_name":              "server2",
 			"retention_period":         "P7D",
-			"backup_intervals":         []string{"R/2024-01-01T00:00:00+00:00/P2D"},
+			"backup_intervals":         []string{"R/2024-01-01T00:00:00+00:00/P1W"},
 			"server_id":                *externalResources.PostgresqlFlexibleServerTwo.ID,
 			"server_resource_group_id": *externalResources.ResourceGroup.ID,
 		},
diff --git a/tests/integration-tests/.terraform.lock.hcl b/tests/integration-tests/.terraform.lock.hcl
index 279276e..b9b7719 100644
--- a/tests/integration-tests/.terraform.lock.hcl
+++ b/tests/integration-tests/.terraform.lock.hcl
@@ -6,6 +6,7 @@ provider "registry.terraform.io/hashicorp/azurerm" {
   constraints = ">= 4.18.0, < 5.0.0"
   hashes = [
     "h1:/Mwep7xvjuaQvT0cSmCJRwn4bJhPQRFYN/a9Jq+nWDs=",
+    "h1:ct8QFejdwiSb0+Q0DyuvPdVjlSZ8lOOKz/NXuegQ/dE=",
     "zh:3504c2142661ecb0dae71e38b2eb8e1766f7abd08e1979b599d5c52961e84f3c",
     "zh:49ad233a9506ca6815b014b5c7eb0b68c152dd1deac5763e519cebadcbad5259",
     "zh:58daec6f8ab1ebf60755585084a3390a25fbae2f11b39ea925037b0d510faf9b",
@@ -26,6 +27,7 @@ provider "registry.terraform.io/hashicorp/random" {
   constraints = "3.7.2"
   hashes = [
     "h1:0hcNr59VEJbhZYwuDE/ysmyTS0evkfcLarlni+zATPM=",
+    "h1:Def/iHM4HihJCIxQ8AYoxtoVL5lVlYx0V7bX91pxwgM=",
     "zh:14829603a32e4bc4d05062f059e545a91e27ff033756b48afbae6b3c835f508f",
     "zh:1527fb07d9fea400d70e9e6eb4a2b918d5060d604749b6f1c361518e7da546dc",
     "zh:1e86bcd7ebec85ba336b423ba1db046aeaa3c0e5f921039b3f1a6fc2f978feab",
diff --git a/tests/integration-tests/backup_modules_blob_storage.tftest.hcl b/tests/integration-tests/backup_modules_blob_storage.tftest.hcl
index 0344149..b149edd 100644
--- a/tests/integration-tests/backup_modules_blob_storage.tftest.hcl
+++ b/tests/integration-tests/backup_modules_blob_storage.tftest.hcl
@@ -32,7 +32,7 @@ run "create_blob_storage_backup" {
       backup2 = {
         backup_name                = "storage2"
         retention_period           = "P7D"
-        backup_intervals           = ["R/2024-01-01T00:00:00+00:00/P2D"]
+        backup_intervals           = ["R/2024-01-01T00:00:00+00:00/P1W"]
         storage_account_id         = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.Storage/storageAccounts/sastorage2"
         storage_account_containers = ["container2"]
       }
@@ -125,7 +125,7 @@ run "create_blob_storage_backup" {
   }
 
   assert {
-    condition     = module.blob_storage_backup["backup2"].backup_policy.backup_repeating_time_intervals[0] == "R/2024-01-01T00:00:00+00:00/P2D"
+    condition     = module.blob_storage_backup["backup2"].backup_policy.backup_repeating_time_intervals[0] == "R/2024-01-01T00:00:00+00:00/P1W"
     error_message = "Blob storage backup policy backup intervals not as expected."
   }
 
@@ -254,6 +254,64 @@ run "validate_backup_intervals" {
   ]
 }
 
+run "validate_backup_intervals_invalid_frequency" {
+  command = plan
+
+  module {
+    source = "../../infrastructure"
+  }
+
+  variables {
+    resource_group_name        = run.setup_tests.resource_group_name
+    resource_group_location    = "uksouth"
+    backup_vault_name          = run.setup_tests.backup_vault_name
+    log_analytics_workspace_id = run.setup_tests.log_analytics_workspace_id
+    tags                       = run.setup_tests.tags
+    blob_storage_backups = {
+      backup1 = {
+        backup_name                = "storage1"
+        retention_period           = "P7D"
+        backup_intervals           = ["R/2024-01-01T00:00:00+00:00/P2D"]
+        storage_account_id         = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.Storage/storageAccounts/sastorage1"
+        storage_account_containers = ["container1"]
+      }
+    }
+  }
+
+  expect_failures = [
+    var.blob_storage_backups,
+  ]
+}
+
+run "validate_backup_intervals_invalid_structure" {
+  command = plan
+
+  module {
+    source = "../../infrastructure"
+  }
+
+  variables {
+    resource_group_name        = run.setup_tests.resource_group_name
+    resource_group_location    = "uksouth"
+    backup_vault_name          = run.setup_tests.backup_vault_name
+    log_analytics_workspace_id = run.setup_tests.log_analytics_workspace_id
+    tags                       = run.setup_tests.tags
+    blob_storage_backups = {
+      backup1 = {
+        backup_name                = "storage1"
+        retention_period           = "P7D"
+        backup_intervals           = ["P1D", "R/bad-date/P1D", "R/2024-01-01T00:00:00+00:00/PT10H"]
+        storage_account_id         = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.Storage/storageAccounts/sastorage1"
+        storage_account_containers = ["container1"]
+      }
+    }
+  }
+
+  expect_failures = [
+    var.blob_storage_backups,
+  ]
+}
+
 run "validate_storage_account_containers" {
   command = plan
 
diff --git a/tests/integration-tests/backup_modules_managed_disk.tftest.hcl b/tests/integration-tests/backup_modules_managed_disk.tftest.hcl
index e6cee41..a18e334 100644
--- a/tests/integration-tests/backup_modules_managed_disk.tftest.hcl
+++ b/tests/integration-tests/backup_modules_managed_disk.tftest.hcl
@@ -35,7 +35,7 @@ run "create_managed_disk_backup" {
       backup2 = {
         backup_name      = "disk2"
         retention_period = "P7D"
-        backup_intervals = ["R/2024-01-01T00:00:00+00:00/P2D"]
+        backup_intervals = ["R/2024-01-01T00:00:00+00:00/PT12H"]
         managed_disk_id  = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.Compute/disks/disk-2"
         managed_disk_resource_group = {
           id   = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group2"
@@ -131,7 +131,7 @@ run "create_managed_disk_backup" {
   }
 
   assert {
-    condition     = module.managed_disk_backup["backup2"].backup_policy.backup_repeating_time_intervals[0] == "R/2024-01-01T00:00:00+00:00/P2D"
+    condition     = module.managed_disk_backup["backup2"].backup_policy.backup_repeating_time_intervals[0] == "R/2024-01-01T00:00:00+00:00/PT12H"
     error_message = "Managed disk backup policy backup intervals not as expected."
   }
 
@@ -268,3 +268,67 @@ run "validate_backup_intervals" {
     var.managed_disk_backups,
   ]
 }
+
+run "validate_backup_intervals_invalid_frequency" {
+  command = plan
+
+  module {
+    source = "../../infrastructure"
+  }
+
+  variables {
+    resource_group_name        = run.setup_tests.resource_group_name
+    resource_group_location    = "uksouth"
+    backup_vault_name          = run.setup_tests.backup_vault_name
+    log_analytics_workspace_id = run.setup_tests.log_analytics_workspace_id
+    tags                       = run.setup_tests.tags
+    managed_disk_backups = {
+      backup1 = {
+        backup_name      = "disk1"
+        retention_period = "P7D"
+        backup_intervals = ["R/2024-01-01T00:00:00+00:00/P2D"]
+        managed_disk_id  = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.Compute/disks/disk-1"
+        managed_disk_resource_group = {
+          id   = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group1"
+          name = "example-resource-group1"
+        }
+      }
+    }
+  }
+
+  expect_failures = [
+    var.managed_disk_backups,
+  ]
+}
+
+run "validate_backup_intervals_invalid_structure" {
+  command = plan
+
+  module {
+    source = "../../infrastructure"
+  }
+
+  variables {
+    resource_group_name        = run.setup_tests.resource_group_name
+    resource_group_location    = "uksouth"
+    backup_vault_name          = run.setup_tests.backup_vault_name
+    log_analytics_workspace_id = run.setup_tests.log_analytics_workspace_id
+    tags                       = run.setup_tests.tags
+    managed_disk_backups = {
+      backup1 = {
+        backup_name      = "disk1"
+        retention_period = "P7D"
+        backup_intervals = ["P1D", "R/bad-date/P1D", "R/2024-01-01T00:00:00+00:00/PT10H"]
+        managed_disk_id  = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.Compute/disks/disk-1"
+        managed_disk_resource_group = {
+          id   = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group1"
+          name = "example-resource-group1"
+        }
+      }
+    }
+  }
+
+  expect_failures = [
+    var.managed_disk_backups,
+  ]
+}
diff --git a/tests/integration-tests/backup_modules_postgresql_flexible_server.tftest.hcl b/tests/integration-tests/backup_modules_postgresql_flexible_server.tftest.hcl
index c33bd39..27754ac 100644
--- a/tests/integration-tests/backup_modules_postgresql_flexible_server.tftest.hcl
+++ b/tests/integration-tests/backup_modules_postgresql_flexible_server.tftest.hcl
@@ -25,14 +25,14 @@ run "create_postgresql_flexible_server_backup" {
       backup1 = {
         backup_name              = "server1"
         retention_period         = "P1D"
-        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1D"]
+        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1W"]
         server_id                = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.DBforPostgreSQL/flexibleServers/server-1"
         server_resource_group_id = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group1"
       }
       backup2 = {
         backup_name              = "server2"
         retention_period         = "P7D"
-        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P2D"]
+        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1W"]
         server_id                = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.DBforPostgreSQL/flexibleServers/server-2"
         server_resource_group_id = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group2"
       }
@@ -65,7 +65,7 @@ run "create_postgresql_flexible_server_backup" {
   }
 
   assert {
-    condition     = module.postgresql_flexible_server_backup["backup1"].backup_policy.backup_repeating_time_intervals[0] == "R/2024-01-01T00:00:00+00:00/P1D"
+    condition     = module.postgresql_flexible_server_backup["backup1"].backup_policy.backup_repeating_time_intervals[0] == "R/2024-01-01T00:00:00+00:00/P1W"
     error_message = "Postgresql flexible server backup policy backup intervals not as expected."
   }
 
@@ -120,7 +120,7 @@ run "create_postgresql_flexible_server_backup" {
   }
 
   assert {
-    condition     = module.postgresql_flexible_server_backup["backup2"].backup_policy.backup_repeating_time_intervals[0] == "R/2024-01-01T00:00:00+00:00/P2D"
+    condition     = module.postgresql_flexible_server_backup["backup2"].backup_policy.backup_repeating_time_intervals[0] == "R/2024-01-01T00:00:00+00:00/P1W"
     error_message = "Postgresql flexible server backup policy backup intervals not as expected."
   }
 
@@ -172,7 +172,7 @@ run "validate_retention_period" {
       backup1 = {
         backup_name              = "server1"
         retention_period         = "P30D"
-        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1D"]
+        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1W"]
         server_id                = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.DBforPostgreSQL/flexibleServers/server-1"
         server_resource_group_id = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group1"
       }
@@ -202,7 +202,7 @@ run "validate_retention_period_with_extended_retention" {
       backup1 = {
         backup_name              = "server1"
         retention_period         = "P30D"
-        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1D"]
+        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1W"]
         server_id                = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.DBforPostgreSQL/flexibleServers/server-1"
         server_resource_group_id = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group1"
       }
@@ -243,3 +243,61 @@ run "validate_backup_intervals" {
     var.postgresql_flexible_server_backups,
   ]
 }
+
+run "validate_backup_intervals_invalid_frequency" {
+  command = plan
+
+  module {
+    source = "../../infrastructure"
+  }
+
+  variables {
+    resource_group_name        = run.setup_tests.resource_group_name
+    resource_group_location    = "uksouth"
+    backup_vault_name          = run.setup_tests.backup_vault_name
+    log_analytics_workspace_id = run.setup_tests.log_analytics_workspace_id
+    tags                       = run.setup_tests.tags
+    postgresql_flexible_server_backups = {
+      backup1 = {
+        backup_name              = "server1"
+        retention_period         = "P7D"
+        backup_intervals         = ["R/2024-01-01T00:00:00+00:00/P1D"]
+        server_id                = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.DBforPostgreSQL/flexibleServers/server-1"
+        server_resource_group_id = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group1"
+      }
+    }
+  }
+
+  expect_failures = [
+    var.postgresql_flexible_server_backups,
+  ]
+}
+
+run "validate_backup_intervals_invalid_structure" {
+  command = plan
+
+  module {
+    source = "../../infrastructure"
+  }
+
+  variables {
+    resource_group_name        = run.setup_tests.resource_group_name
+    resource_group_location    = "uksouth"
+    backup_vault_name          = run.setup_tests.backup_vault_name
+    log_analytics_workspace_id = run.setup_tests.log_analytics_workspace_id
+    tags                       = run.setup_tests.tags
+    postgresql_flexible_server_backups = {
+      backup1 = {
+        backup_name              = "server1"
+        retention_period         = "P7D"
+        backup_intervals         = ["P1D", "R/bad-date/P1D", "R/2024-01-01T00:00:00+00:00/PT10H"]
+        server_id                = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group/providers/Microsoft.DBforPostgreSQL/flexibleServers/server-1"
+        server_resource_group_id = "/subscriptions/12345678-1234-9876-4563-123456789012/resourceGroups/example-resource-group1"
+      }
+    }
+  }
+
+  expect_failures = [
+    var.postgresql_flexible_server_backups,
+  ]
+}