Hoping you are still around and see my comment here. I have a Flutter project where I have implemented a softphone using the sip_ua package. Everything is working fine, except exactly the scenario you called out above here. For iOS only, the problem is that there is only 1 way audio. The caller to the softphone can hear audio coming out from it, but the audio coming from the caller into the softphone cannot be heard. I have ensured this is not a permissions issue. I also have looked at the network traffic and see audio data flowing both ways. We are using the Opus codec as well.

I want to implement the same fix you provided here, but I dont have enough of an understanding of the mechanics of AppDelegate.swift to implement a complete solution. Would you be able to provide your full AppDelegate.swift so that I can model mine after that? Thanks!