The forum seems deserted. Let’s hope that’s not the case.
Reference this post from ages ago:
I have the same symptom. I have a theory as to how to fix it but not sure if I can with the Grandstream device.
My PBX does not allow me to set the User ID to the phone number. It has a string that correlates to a username and forces me to enter letters. This value works in SIP - I can make and receive calls, it’s just the Caller ID.
Apparently, something in the Grandstream firmware changed to use the User ID for caller ID. Problem is, if you can’t make that numbers, the device doesn’t know what to do about it.
So. I need to figure out how to get this resolved - where I am not able to give it a numeric value for User ID.