Problem FaceTiming one contact

I cannot FaceTime one of my contacts - the icon is not greyed out and there is ringing so he is available, but he doesn’t know I’m calling him. Yet he can Facetime me and I can take his calls. This doesn’t happen with anyone else. I’ve taken various actions - Signed out of Apple ID, deleted the contact and restored it, turned off and on FaceTime, turned off both devices, but no change. Him or me?