Caller hears echo of their voice: Apple Carplay + iPhone12 promax + Boss Boss BE9ACP car stereo

Hello,

This seems to be a common problem. The question shows up in many places, but there have been no answers from Apple or others that seem to solve the problem.

Description:

• Aftermarket (brand new) Boss head unit listed above installed in 2007 Toyota Highlander
• Problem: those talking to me, when I'm speaking with them through system, hear a clear echo of their own voice
• Hands-free microphone installed in different locations, all with same result
• I do not hear any echo, neither mine or theirs
• They do not hear an echo of my voice, only of their voice

NOTE: the problem ALSO occurs when phone connected via Bluetooth.

I have tried with USB/Cartalk connected, and Bluetooth turned off on the phone, just to be sure both systems aren't somehow active. This made no difference.

Am pretty sure this is due to the caller's voice being fed back to them, after it comes out of my car speakers.

Am hoping there is a setting or adjustment to manage this in the iPhone.

There is no such setting in the Boss unit.

Though this seems to be be a problem specific to iPhone, and specifically iPhone 12.

Any suggestions or solutions greatly appreciated.