Question: In a 5G System using the GetGbaAv service operation for GBA Authentication Vector Retrieval, what HTTP status code is returned by the UDM if the user (UE) does not exist?
Option 1: 401 Unauthorized
Option 2: 403 Forbidden
Option 3: 500 Internal Server Error
Option 4: 404 Not Found
Explanation: According to the specified procedure for GBA Authentication Vector Retrieval, if the user (UE) does not exist, the UDM shall respond with an HTTP status code '404 Not Found', indicating that the requested resource could not be found, with additional error information in the 'ProblemDetails' element of the response body.