Kiro Pro Plus subscription fails with backend "UnknownError" (CreateAssignment, q.amazonaws.com)

I understand you're experiencing an "UnknownError" when trying to assign a user to Amazon Q Developer Pro Plus (formerly known as Amazon CodeWhisperer Professional tier). This type of generic error can be frustrating, especially when you've verified your configuration.

Based on the information you've provided, here are some key points to consider:

About Amazon Q Developer Pro Plus Subscriptions: Amazon Q Developer Pro Plus requires an IAM Identity Center organization instance (which you have) and proper subscription management through the AWS Management Console. The subscription allows you to assign licenses to users in your organization.

Common Issues to Verify:

1. IAM Identity Center Configuration: Ensure your IAM Identity Center organization instance is fully set up and that the user exists and is active in the directory
2. Subscription Status: Verify that your Amazon Q Developer subscription is active and that you have available licenses to assign
3. Regional Consistency: Confirm all resources (IAM Identity Center, Amazon Q subscription) are in the same region (us-east-1 in your case)
4. User State: Ensure the user account is in a valid state and not in a transitional status from your recent migration

For Backend/Service Issues: If you've verified all configuration elements and the error persists, this could indicate a service-side issue that requires AWS Support investigation. The "UnknownError" with no specific details often requires backend troubleshooting that only AWS Support can perform with access to internal service logs.

Next Steps: I recommend opening a support case through the AWS Support Center (https://console.aws.amazon.com/support/) where you can provide the Request ID and CloudTrail details you've collected. The support team can investigate whether there are any account-level restrictions or backend provisioning issues preventing the subscription assignment. Include all the diagnostic information you've gathered, as this will help expedite the investigation.

Your AWS Support plan level will determine response times, so you may want to review your support plan options if you need faster assistance with production-impacting issues.