Carplay Issues

I Have just updated the media unit in my car to Carplay

I have an Iphone 12 Pro Max with the latest updates.

I can make/receive phone calls using Car Play with no issues, nice clear audio, except when I call my wife's IPhone 12 Pro Max. I can see on the screen, the Device is making the call, but there is no audio at all.

I can not hear the ring tone or both of us hear each other.

Its the same when I connect my wife's iPhone to the CarPlay, no audio at all when I call my iPhone.

It is only our two phones that have the audio issues. I called my iPhone 7 (I use for work) using both phones with no issues.

When I disconnect the Carplay and connect to the Media Unit via Bluetooth there are no issues with both phones.

I have gone through the settings on both phones tp make sure thy are set the same.

Is there something I'm missing, a setting that turns off Carplay ???