I use Zoiper 5 VOIP phone (Free version) and number is via Buzz Box.
I have set it up on MacOs Sequoia 15.5.
When a call comes in and I click on the 'green' to pick it up, it just doesn't respond. No error messages and calls just keeps ringing. I have to disconnect and then call back.
It has been working fine till may be Feb - March this year, but then this issue started to appear.
I have tried to uninstall, reinstall it more than once but issue persists.
Not sure but it may have started to happen after one of the OS updates since March 2025.