My iPhone 6 can't send a group message to an iPhone 5 but individual texts work. How can I set this up?

[iMore Question]

My iphone 6 can't send a group message to an iphone 5, but individual texts work

I am on AT&T, the other phone is on Verizon. I have tried Imessage and 2 group text apps with the same result. With the group app I see an invalid number message. Others in the group receive the texts just fine.

 

[Bigeric23]

Re: My iphone 6 can't send a group message to an iphone 5, but individual texts work

Does this work with other people you text?

 

[Just_Me_D]

Re: My iphone 6 can't send a group message to an iphone 5, but individual texts work

I am on AT&T, the other phone is on Verizon. I have tried Imessage and 2 group text apps with the same result. With the group app I see an invalid number message. Others in the group receive the texts just fine.

What 'group app' are you referring to?