Messages to a friend go out as text rather than iMessage after they changed their phone number
Hi, the number of a friend of mine switched from a German mobile number to a US number. I've updated their contact card (but retained the old German number as "other"). They use an iPhone and are signed into iMessage. I can send a direct, person-to-person iMessage to them, but when I try to send a message to an existing group, it goes out as text. So I tried to create a new group, selecting my friend by their new US number. It still goes out as text.
Does anyone have any ideas about what's going on here?
Thanks!
iPhone 15 Pro, iOS 18