Phone app unable to make calls

If I try to make a call on the Phone app I immediately get a message 'iPhone calls not available, Your iPhone must use the same iCloud and FaceTime account'. They are and I have done all the obvious things like restarting both devices, signing out of both FaceTime and Phone apps on the Mac and no difference. On the iPhone I have checked that it is enabled to make calls on other devices and it even lists the Mac there so it seems to recognize them as having the same account details.

Any ideas?