Remote extensions no audio


I recently installed asterisk and I have some problems I would be glad if you help me

my local extension can call each other no problem , also I have Sangoma Vega 50 Gateway I can use it to go through PSTN

I configured the remote extension and I can register on my asterisk server no problem also I can call pstn with the remote extension

the remote extension can call the local extension and the audio is very good

my problem is the remote extension can call and ring but when i answer the call no audio coming both extension
I am using Snom phone 710 & 821 I also use soft phone but is the same no sound in remote extension

I solved the problem

my snom phone rtp port was set for another range I put it to my open rang and its working very good now