Does anyone here use SIP calls?

I have a jmp.chat account with a local phone number. It works flawlessly with other programs/apps on other devices that are not the FLX1. However, when I enter the settings into the FLX1 dialer app, it does not allow me to make phone calls out. It does receive phone calls, but I cannot speak to the other party.

If I download the flathub version of Linphone, I can enter the same settings and dial out, calling other people, and receive phone calls. However, again I cannot be heard when speaking to others. I've tried to adjust the sound settings, but don't seem to be getting anywhere. 

Anyone else use SIP calls with the FLX1?