How to have rotation via ffmpeg and 2-way audio at the same time?

I have a doorbell camera (Wyze WVDB1) running Thingino firmware and video from this camera is rotated when the doorbell is mounted in vertical orientation. Trying to rotate it using firmware creates a lot of stream stability issues, so my only option is to rotate it with ffmpeg, however when using this method - I lose 2-way audio, which is also crucial for the doorbell.

I've tried adding #backchannel=1 to the restream, but that does not seem to do anything and the probe for that stream is missing audio, sendonly entries entirely.

Direct stream

my_cam:
  - rtsp://user:[email protected]:554/ch0#timeout=30
  - ffmpeg:my_cam#audio=aac

ffmpeg restream

my_cam_rotated:
  - ffmpeg:my_cam#video=h264#rotate=90#audio=copy#backchannel=1