Issue Summary

The Confluence Cloud REST API endpointAdd member to group by groupId should return a meaningful HTTP error code and message when the operation fails due to a depleted license pool, instead of a generic 500 Internal server Error.

curl --request POST \
  --url 'https://your-domain.atlassian.net/wiki/rest/api/group/userByGroupId?groupId={groupId}' \
  --user 'email@example.com:<api_token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "accountId": "<string>"
}'

Steps to Reproduce

1. Have a Confluence Cloud site with centralized user management enabled

1. Exhaust the available license pool (all seats allocated)

1. Call POST /wiki/rest/api/group/userByGroupId?groupId={groupId} with a valid accountId in the body

1. Observe: 500 error with HystrixRuntimeException instead of a meaningful license-exceeded error

Expected Results

The endpoint should return an appropriate HTTP status code (e.g., 409 Conflict or 403 Forbidden) with a clear, actionable error message such as:
 

{
  "statusCode": 409,
  "message": "Cannot add user to group: Product license limit exceeded. Please free up licenses or upgrade your plan.",
  "errorType": "LicenceExceeded"
} 

This is consistent with how the newer Atlassian Administration API (POST /admin/v1/orgs/{orgId}/directory/groups/{groupId}/memberships) already handles this scenario — returning a proper 409 with title "Product License Limit Exceeded".

Actual Results

When a customer's license pool is exhausted, and they attempt to add a user to a group via the REST API, the endpoint returns:
 
 

{
  "statusCode": 500,
  "message": "com.netflix.hystrix.exception.HystrixRuntimeException: AddUserToGroupsIdentityPlatformCommand failed and no fallback available."
}

Workaround

Alternatively, customers can use the Atlassian Administration API, which already returns proper error codes for this scenario, but this requires a different authentication model and API integration.

the newer Atlassian Administration API (POST /admin/v1/orgs/{orgId}/directory/groups/{groupId}/memberships) does handle this scenario correctly and returns a proper 409 status with a "Product License Limit Exceeded" message. However, I understand you'd prefer not to switch APIs at this time, and that's completely fine.