JSON deep insert returns atom/xml

Dear,

When I test a json deep insert (For eaxmple:a POST on /sap/opu/odata/sap/<Gateway_service>/<GW_Data>Set in the GW Client then it returns the result in atom/xml....

If i add ?$format=json to the call i receive following error:

The Data Services Request contains SystemQueryOptions that are not allowed for this Request Type

Is there a way to get the response in json for a POST deep insert/create?

Thanks in advance!

Kind Regards,

Robin