Hello Samir,
Been away for exams.
My case is simple (plus what I have done):
1. My ASTPP box is already connected to the VoIP provider OK
2. I have established connection between the PBX and ASTPP.
3. I have configured ASTPP as the GW on the PBX and calls are sent out OK
4. Inbound calls however have not worked. I have routed DID via SIP Devices and created a GW (with PBX settings) on ASTPP but inbound doesnt work.
I should mention I have connected the PBX directly to the provider and all works well. DIDs are recieved and dialplan picks it up for routing on the PBX.
This is not yet a commercial setup. Just tests envs running in VMs.