Your wiring looks correct, so not sure why it wouldn’t be working.
Your handset only works with the Came BPT System X1 intercom and Ring Intercom is confirmed working with other System X1 compatible handsets (eg. AGATA VC).
Maybe try configuring Ring Intercom with one of the other System X1 compatible handsets (eg. Agata C, Agata VC) and NOT your YC/300A?
Edit: Sorry, just re-read that entire thread and can see that @BlackDee is saying s/he is having issues (it did seem to work, once). Your best option might be to follow up with ring support as per the final comment from Justin. There’s another AGATA VC (System X1) related issue post here so you could also join that thread (or even the original post from December 2022) as there’s now 3 “not working” System X1-related threads even though the Ring Intercom online compatibility checker CONFIRMS the product is supposed to work with System X1 handsets.