I've faced something similar, that was caused by the provider sending the ACK to the correct IP (kamailio) but the domain of the R-URI was not the FS - which appears to be the case in the traces I've quickly looked at.

In that case, I was forced to tah the dialog in the invite (via htable), and when relaying a method and the ruri was myself, fix the ru and du

On Fri, Apr 20, 2018 at 4:13 AM, Volkan Oransoy <voransoy@gmail.com> wrote:

Hi all,

I have a Kamailio box which I use as a uac_client. We register a bunch of accounts to remote providers. The box relays incoming calls to a FreeSwitch box. We encountered a strange problem on one account.
Kamailio relays the call to my FreeSwitch box successfully but routes the ACK itself which is the reply of 200Ok. I believe this is a provider related issue but I need a technical explanation. Does anyone have any idea?

Here is the packet capture: https://pastebin.com/PA8StiWY

Thanks,

--
Volkan Oransoy

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