I also have exactly same problem
I am having exactly same problem on a new account that I am setting up on my MBP. I am able to send iMessage to A and B but not to C whereas they can send iMessages among each other
Me<->A OK
Me<->B OK
Me<->C NO
A<->B OK
B<->C OK
A<->C OK
A<->B OK
I read all of the responses above and checked that my Messages settings on phone and MBP both are configured as people suggested, yet it doesn't seem to send messages from MBP to one number. I am searching for solutions in this forum and appreciate if anyone can advise something that is not tried yet. TIA
Then if you get the message "not registered", that's something to do with your husbands phone.
I am having exactly same problem on a new account that I am setting up on my MBP. I am able to send iMessage to A and B but not to C whereas they can send iMessages among each other
Me<->A OK
Me<->B OK
Me<->C NO
A<->B OK
B<->C OK
A<->C OK
A<->B OK
I read all of the responses above and checked that my Messages settings on phone and MBP both are configured as people suggested, yet it doesn't seem to send messages from MBP to one number. I am searching for solutions in this forum and appreciate if anyone can advise something that is not tried yet. TIA