The Visca over IP backend does not work with Sony BRC cameras, the messages are missing the required header (Payload type/Payload length/Sequence number). See Sony VISCA over IP document page 10.
https://pro.sony/support/res/manuals/C456/26213181c7ae83822c3124b5b3b836ee/C4561001M.pdf
Midimonster is just sending the "payload" part - this might wor with e.g. PTZOptics cameras, but not with Sony BRC or FR cameras.

Any chance this will be implemented? Maybe an extra backend for Sony PTZ?