All circuits are busy

When we hit 8 “External calls”, all outgoing calls return “All circuits are busy” message.
Our main Outbound Route contains 11 Trunk Sequences. Shouldn’t that give us 11 simultaneous outgoing calls?

Nope - 11 sequences give you 11 sequences. The number of simultaneous calls is completely unrelated. The trunk will have a limit (anywhere from 1 to unlimited, depending on technology), but the outbound routes do not care.

Check you /var/log/asterisk/full log to see why the ACB message is getting generated.

I’m getting “chan_sip.c: Received response: “Forbidden” from '<sip:[email protected]

Maybe our VoIP provider doesn’t allow outgoing calls on all lines?

Have you called your provider and asked them? They can tell you with certainty what the problem is.