Whatsapp audio error to ONE CONTACT ONLY

Hello,
I have an issue with my whatsapp call, whenever I called my boyfriend the audio is error (silent) I can’t hear him and he can hear me. but this happened only with my boyfriend contact. I tried to call others and it’s fine, no audio issues. I also try to call from regular mobile data and it’s fine so the issue is only on whatsapp call and only with my boyfriend’s contact. He is experiencing the same with my contact. What happened? How to fix this?