Ring Intercom doesn’t work on CAME BPT Opale

I’m pretty confident that I’ve correctly wired Ring Intercom to the bus CAME BPT Opale White system, which is listed on Ring’s site as compatible. I’ve read the intercom schematic and tried a few different combinations, and other people have had success with B1/B2 into each of the two “B” Bus ports. However, when testing, the Ring device is never able to answer the call from our intercom. It does try to respond - you can tell because the screen flashes when Ring Intercom communicates with our primary intercom unit, and when I answer the call manually you can hear Ring’s test audio through the speaker. It works, but it can’t pick up. Ring Intercom is also able to correctly identify that a call is incoming – when I continued with setup as a test (even though it wasn’t working properly), I did correctly receive push notifications for incoming calls. However, without manual intervention, Ring Intercom is unable to pick up any incoming calls, meaning it cannot unlock the door or answer the intercom request. In other words, it’s pretty much useless right now. I’ve contacted Ring Support but does anybody have ideas on how to solve this? Or are Ring just totally mis-selling “compatibility”?