Allows a buyer from an external DSP to get the creatives that were sent for approval with the specified creative id.
Since the same creative id can be used for different publishers, the endpoint could return multiple
creatives. To avoid this behaviour, the user can specify a publisher ID in the corresponding query string.
In Hivestack, creative approval is done at the creative file level. The approval status
can be retrieved in the approval_state of the returned media files. Only the approved media files
will be selected to play.
The approval_state allows 3 different integer values. They are: