Can’t “Allow calls on other devices” despite all settings looking right
I have set up "allow calls on other devices" on my mother's new iPhone. On the new iPhone I have allowed calls to go to her MacBook and her Old iPhone.
On the MacBook, calls come through no problem.
On the Old iPhone, calls never ring through. If I try to make a call from that phone, I get "Call Failed" and a big X. This phone was just updated to iOS 15.7.7 to try solving this. It's logged in to iCloud, Facetime is active.
Facetime calls come through to the Old iPhone, but not cell phone calls.
The old iPhone is a 6s Plus. The new phone is a 13 Pro.
iPhone 6s, iOS 15