Fax Machine works when ATA configured direct, but not throught FreePBX

I’m running the FreePBX Distro 5.211.65.

I have a fax machine hooked up to an Analog Terminal Adapter (the Obi 100).

When I configure the Obi to connect directly to a ITSP, like VOIP.ms/Flowroute/etc, faxes go through flawlessly.

But, when I configure the Obi to connect to my machine running FreePBX/Asterisk (which then sends the faxes out to the same ITSP), the faxes choke and almost always fail.

I’ve verified that calls are going from Obi to Asterisk and from Asterisk to ITSP using ULaw.

Can anyone think of any configuration change that I might make, or place I might look, to find out why ATA to ITSP works, but ATA to Asterisk to ITSP does not?

Ensure t38 pass-through is enabled

I don’t think that’s it. The ITSP that I’m using doesn’t support T.38…