[Bug][SubscriptionBilling]: Credit Memo cannot be posted after Service Commitment Option is changed on item

[miljance]

Describe the issue

When an item's Subscription Option is changed after it has already been sold and invoiced, posting a credit memo against the original invoice fails with an error related to the changed option.

Expected behavior

It should be possible to post a credit memo against an invoice regardless of subsequent changes to the item's Subscription Option. The option at the time of the original posting should be used for the reversal.

Steps to reproduce

1. Create and sell an item with Subscription Option set to No Subscription.
2. Post the sales invoice.
3. Change the item's Subscription Option to Subscription Item.
4. Create a credit memo for the original invoice and attempt to post it.
   • ❌ Result: Posting fails with an error related to the Subscription Option.

Additional context

No response

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• I will provide a fix for a bug