diff --git a/app/oauth.py b/app/oauth.py
index 0f4793c..6c1889c 100644
--- a/app/oauth.py
+++ b/app/oauth.py
@@ -6,6 +6,7 @@
 from functools import lru_cache
 
 import jwt
+import structlog
 from cryptography.hazmat.primitives import serialization
 from cryptography.hazmat.primitives.asymmetric.rsa import RSAPublicNumbers
 from fastapi import APIRouter, Form, HTTPException, Request
@@ -15,6 +16,7 @@
 from app.config import get_settings
 
 router = APIRouter()
+_log = structlog.get_logger()
 
 TOKEN_TTL = 24 * 3600
 KEY_ID = "mem0-oauth-1"
@@ -89,7 +91,10 @@ def _as_metadata() -> dict:
 def _protected_resource_metadata() -> dict:
     base = get_settings().public_base_url.rstrip("/")
     return {
-        "resource": f"{base}/mcp/",
+        # Canonical resource URI per the MCP auth spec: omit the trailing slash.
+        # MCP clients (Claude.ai / Cowork) canonicalize to the no-slash form and
+        # reject authorization if the advertised resource doesn't match.
+        "resource": f"{base}/mcp",
         "authorization_servers": [base],
         "scopes_supported": SCOPES,
         "bearer_methods_supported": ["header"],
@@ -128,7 +133,17 @@ async def register(request: Request) -> JSONResponse:
     body = await request.json()
     redirect_uris = body.get("redirect_uris") or []
     allowed = set(get_settings().allowed_redirect_uris_list)
-    if not redirect_uris or any(uri not in allowed for uri in redirect_uris):
+    rejected = [uri for uri in redirect_uris if uri not in allowed]
+    if not redirect_uris or rejected:
+        # Log the exact requested URIs and the active allowlist so a client whose
+        # callback isn't allowed (the common cause of failed Claude.ai / Cowork
+        # connections) can be diagnosed and added to OAUTH_ALLOWED_REDIRECT_URIS.
+        _log.warning(
+            "dcr_redirect_uri_rejected",
+            requested=redirect_uris,
+            rejected=rejected,
+            allowed=sorted(allowed),
+        )
         raise HTTPException(status_code=400, detail="redirect_uri not allowed")
     # Register as a public client: PKCE (S256) protects the code exchange, so
     # no client_secret is issued or verified.
diff --git a/docs/USER_GUIDE.md b/docs/USER_GUIDE.md
index c03c426..335a198 100644
--- a/docs/USER_GUIDE.md
+++ b/docs/USER_GUIDE.md
@@ -302,4 +302,5 @@ status, and latency. The `Authorization` header is never logged.
 | Server won't start | A required env var is missing or a provider key is absent. Check the startup logs; `app/config.py` names the missing variable. |
 | Claude.ai web / Cowork can't connect | OAuth not enabled (`OAUTH_SIGNING_KEY` blank), or the client's redirect URI isn't in `OAUTH_ALLOWED_REDIRECT_URIS`. |
 | "Couldn't reach the MCP server" on Claude.ai web / Cowork (but Claude Code/Desktop work) | OAuth discovery failure. Confirm `OAUTH_SIGNING_KEY` is set and `PUBLIC_BASE_URL` exactly matches the public HTTPS URL; the server must advertise the protected-resource metadata in the `/mcp/` 401 `WWW-Authenticate` header. |
+| Connector fails right after consent; logs show `POST /oauth/register → 400` | The client's callback isn't in `OAUTH_ALLOWED_REDIRECT_URIS`. The server logs a `dcr_redirect_uri_rejected` warning with the exact `requested` URI and the active `allowed` list — add the requested URI to `OAUTH_ALLOWED_REDIRECT_URIS` and redeploy. Claude.ai web/desktop/mobile/Cowork use `https://claude.ai/api/mcp/auth_callback`. |
 | Backup job not running | Check the backup container: `caprover logs mem0-backup`. |
diff --git a/tests/test_oauth.py b/tests/test_oauth.py
index 1639bed..8df661d 100644
--- a/tests/test_oauth.py
+++ b/tests/test_oauth.py
@@ -69,7 +69,7 @@ def test_protected_resource_metadata(oauth_client):
         "/.well-known/oauth-protected-resource/mcp",
     ):
         meta = oauth_client.get(path).json()
-        assert meta["resource"] == "https://mem0.test/mcp/"
+        assert meta["resource"] == "https://mem0.test/mcp"
         assert meta["authorization_servers"] == ["https://mem0.test"]
         assert meta["bearer_methods_supported"] == ["header"]
         assert meta["scopes_supported"] == ["read", "write"]
@@ -404,7 +404,7 @@ async def lifespan(app):
             assert meta_resp.status_code == 200, (
                 f"{urlparse(rm_url).path} returned {meta_resp.status_code}, not a direct 200"
             )
-            assert meta_resp.json()["resource"].endswith("/mcp/")
+            assert meta_resp.json()["resource"].endswith("/mcp")
     finally:
         # monkeypatch handles env restoration; lru_caches must be cleared manually
         # so other tests don't observe OAuth-enabled settings.