They are definitely saying inbound trunk, which means the trunk from you, but, as this is not a standard SIP message, it is not easy to say why they think it is faulty.
Taken at face value, I would say that they already thought your trunk was down before you tried to issue the INVITE.
If they won’t help you, do you know what they use to implement their service. Maybe you can find some documentation that explains what the numbers in the message mean.
Wildly guessing, you might be marked as down because you haven’t registered (many systems require that for calls to be accepted, even though SIP doesn’t), or that they’ve done a connectivity test, e.g. with OPTIONS, that has failed.
Is there any reason why you are using the, effectively unsupported chan_sip, and a definitely unsupported version of Asterisk?
Where did you get your sip.conf settings from? They show most of the typical bad practice (low security, obsolete options, ineffective options, and unneeded workarounds) that are common with provider supplied configurations. However, I don’t think any of those are causing your problem.
These configuration are provided by service provider.
Since it is private link not on public network that is why authentication is not an issue.
The trunk is up and online that is why inbound calls are being received,
IAC*CLI> sip show peers
Name/username Host Dyn Forcerport Comedia ACL Port Status Description
000/000 192.168.1.38 D No No 62196 OK (108 ms)
001/001 (Unspecified) D No No 0 UNKNOWN
002/002 (Unspecified) D No No 0 UNKNOWN
003/003 (Unspecified) D No No 0 UNKNOWN
004/004 (Unspecified) D No No 0 UNKNOWN
005/005 (Unspecified) D No No 0 UNKNOWN
04232590040/04232590040 10.200.57.112 Yes Yes 5060 OK (43 ms)
101/101 (Unspecified) D No No 0 UNKNOWN
If any other setting can be helpful to change please let me know.
Note that allow=all, definitely results in excessively large INVITE requests, and at least in some circumstances results in failures, although I seem to remember that it is the Asterisk end that fails.
A 404 still confirms that you are reachable and Asterisk would accept that. However, I suppose it is possible that they only intended for phones, not PABXes, and insist on an OK. However, I think that would stop them sending to you.