Problems in talk stream Start a WebRTC connection

Hello,
I have some problems in this request. I'm creating a stream and getting data from the response successfully. Then I'm trying to make the next request for starting a WebRTC connection and I always get 400 error because of incorrect session id, or incorrect answer object. Then I've written some code to make a peer connection with ice servers and ice candidates. And then I'm getting the error "aiortc.exceptions.operationerror: failed to set remote video description send parameters". I've read that it can be caused by H264 codecs in SDP object. I've removed them, but it hasn't helped at all.
I'm writing with python, using aiortc.
Could you please advise me something?