Facetime no video or audio from the recipient

When I make contact with my son via Facetime, he can answer the call. He is able to hear en see me, but I don't. He always then end the conversation and the he calls me. Then we can use Facetime in the way it is supposed to be.

We both use the latest version IOS.

Ik have a iPhone 16 pro. He has an old one iPhone 9.