T25 & Grandstream GXV3140

Hi guys,

I want to use my GXV 3140 (FW together with my T25 (MX-V4.7.3.11). In order to do so I configured it using Auto Configuration. Both T25 and GXV were set to default settings before running auto config.
Everything was configured, and almost everything is working: GXV was found and configured.
Just one thing which currently is the only remaining issue:
As soon as somebody is ringing the bell, an incoming call at GXV is shown. But it is just ringing and showing an incoming call on the display of GXV. As soon as I am trying to accept the call nothing is happening. the call is not connected. The display is showing an incoming call until I am restarting the GXV. It is still reachable in browser and can be configured in browser but the display is showing an incoming call until restart.
Once I am calling the T25 from GXV → same thing.
Is there anybody who had similar issues?