Hi,
it was the reason for me. As stated in Enabling Media Links - SAP NetWeaver Gateway Foundation (SAP_GWFND) - SAP Library - Media type is only supported for feed and entry. You should redefine the method DEFINE() of the model provider extension class generated by the SB to avail the media link functionality.
So it seems that create_entity and get_entity_list works, but in order to make get_entity work you need to redefine MPC_EXT. And after create_entity you need to call get_entity in the code to get successful response from gateway after upload.
Best regards,
Peter
