488 Not Acceptable Here

I’m trying to send fax through sip trunk, using Asterisk version 15.4.0. If I don’t use stasis, everything works fine, the trunk switch receives a T.38 re-invite from destination and sends that to load-balancer, it goes to source switch, gets 200-OK response and the process of sending fax begins. But if I bring ARI in, after receiving
T.38 re-invite, trunk switch responses with “488 Not acceptable here”.
What’s the problem and how can I fix it?

I attached 2 log files, one for working part, and another for not working part, and also sip.conf and extensions.conf files.

extensions.conf.txt (363 Bytes)
fax_debug_ari.txt (30.5 KB)
sip.conf.txt (845 Bytes)
fax_debug_ast.txt (38.2 KB)

I believe it’s because you are recording the bridge, which turns it into a multiparty bridge and those do not support T.38 passthrough.

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You’re right, that’s the reason. What do you think I should do if I wanna keep the recording for calls and send fax sometimes?
To my knowledge, I can’t check if it’s T.38 or not at the beginning.

Instead of recording the bridge you could use a snoop channel and record a channel itself, that shouldn’t prevent the fax from working.

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