Error AADB2C90063 While Creating Custom Extension in Entra ExternalID

In the process of developing a custom extension based on the guidance from the Custom Extension Configuration documentation, an error is consistently encountered:

{
    "error": {
        "code": "AADB2C90063",
        "message": "There is a problem with the service.",
        "innerError": {
            "correlationId": "e796fae9-0a95-4605-81b9-f75ad9015f31",
            "date": "2025-05-23T16:54:11",
            "request-id": "8c029e5e-67b8-42a2-866e-29d36f22c6c4",
            "client-request-id": "8c029e5e-67b8-42a2-866e-29d36f22c6c4"
        }
    }
}

The following roles are held:

Attempts to achieve the same result using Microsoft Graph have also been unsuccessful.

Any insights or suggestions would be appreciated!

Thanks