Bad Request Response

I have a Shelly 2.5 and use it as a roller shutter.

Using browser access the API works just fine. But I have an embedded device where I send HTTP requests using a simple sendtcp command. Other devices work well, but Shelly responds with "400 Bad request" without any additional error specification.

Because my proprietary device doesn't has so many debug capabilities, it would be extremely helpful to understand what could cause the Shelly to respond with "400 Bad Request". Or any sort of debugging access, log access or whatever to see the pure bytes received through Wifi.

The Shelly itself isn't probably the issue here, as it responds properly to other clients. But my device works with other servers, so I don't see my device as the root cause, too.

Thanks for any idea or pointer.

Solved with Wireshark. It was indeed a not properly created HTTP package.

Thanks a lot.