Permission error when accessing cloud API

Hi,

I am trying to switch on a relay via the cloud API, based on this documentation. For testing purposes I use Postman. For device id I use the alphanumeric id that the app gives me, for authentication key, the cloud authentication key also from the app. When sending the request, I get an error "Could not control this relay channel!". I tried 0 for channel, as per the documentation, but also tried 1 or omitting the channel, all lead to the same error.

Any idea of what I could be doing wrong?

Problem is already solved - by mistake I put the parameters in the URL instead of the body. After changing that it works as expected!