Silence when transferring a call from mobile to mobile. What could be the reason?

Question

Telephony

Hello!
The problem is this: there is a server with FreeSwitch, the Digium G800 acts as a gateway. When you receive an incoming call from a mobile phone and then transfer it to another mobile phone, there is silence in the handset. When transferring calls according to the scheme “Int. number - Int. number - mobile" no problem. When transferring calls according to the scheme "Mobile - GTS number - ext. number" no problem either.