Unable to call VTH2421FB from VTO3211D

[Agha]

I got a VTO3211D-P4 and a VTH2421FB-P
Both of them are brand new.
VTO unit has the old v1.0 Web Server with 3.200.0012001.0.R firmware.
I managed to update it to the v4.4, Plus, I am able to access the web interface, etc, etc... The only major problem is that I couldn't receive any calls on the VTH (v4.41) unit from the VTO. I can see the video feed on the VTH, I can unlock but I couldn't receive any calls on the VTH unit.
The sign in the upper right hand side of the VTH unit screen is the same on both units... A VTO unit with an X on it.

Please help me out to find a way to make them work together.
Thank you !

 

[Kiefer]

sip server on vth not properly configured.

Ip address: ip from vto
reg pwd: 123456
username: username of vto (admin
pwd: pwd of vto

check also in vto room nr management if there is a room added; try to add 9901#0
make sure on vth room nr is the same