Yealink W52P One Way Audio on Outgoing DAHDI Calls

Hi. I’ve added two Yealink W52P phones to my system (FreePBX 13.0.190.2) today, but I’m having audio issues on outgoing DAHDI calls. With internal calls, audio works fine both ways. When RECEIVING a call on a W52P, audio works fine both ways. Just when making an external call, I can’t hear the other end, yet they can hear me.

I’ve viewed various existing posts about similar issues, but I’ve failed to get anywhere. The SIP and RTP ports are open on the router, however both of the W52Ps are on the same network as the FreePBX server anyway (all on 192.168.0.x).

All other SIP phones are working fine. It’s just the two W52Ps that I’ve added today.

Any advice anyone? Thanks in advance.

Just to add, the connectivity I have is PSTN lines on an FXO card.