C SDK edge services not working

Hi, I'm using the C SDK on an embedded linux platform serving as gateway to collect and push data into the Thingworx platform. The data is already floating into the cloud and I can see it in my dashboards. But I need to be able to call a service on the remote device as well as file transferring, and it seems the device is not reacting to any calls from the platform.

How can I figure out, where the problem is located?

I followed along the Developer Guide to setup my service and the FT on the device, without success. I cannot even use the Test button of the GetRemoteMetadata service inherited by the RemoteThing template...