OBi312 to Valcom 1109RTVA

I have configured my OBi312 successfully & can send/receive calls through my RingCentral SIP account. When I connect a phone to the phone port I can make and receive calls with bi-directional traffic sounding fine. I now want to connect the device to my Valcom 1109RTVA overhead page controller. I have plugged in the controller to the line port on the OBi, but it never picks up when called. It shows TipRingVoltage at 23V but it never picks up. The previous ATA I had was able to work properly, so I know it did work ~2 months ago. Does anybody have any ideas?