Help with Call Forwading

[myhola]

Why every time I set an extension to forward a call to an external number, the call is immediately terminated?
I have a DID number attached to my 3cx. Any help will really be appreciate.

To make it easier:

When someone call my DID (214.xxx.xxxx) which is attached to one of my extension (12007), after 15 secondes the call is set to be forward to my personal Mobile Phone Number. But the system (3cx) terminate the call.

Thank you

 

[archie]

If you have only one PSTN line - PBX can not transfer the call - the only line is busy by incoming call.