Unlocked AT&T Lumia 1520 on Telus network in Canada. Unable to send or receive MMS messages. How can I get this to work?

[Windows Central Question]

Unlocked AT&T Lumia 1520 on Telus network in Canada. Unable to send or receive MMS mesages.

I bought the 1520 to use in Canada on Telus. I entered all of the settings APN, Internet and MMS. Everything is working great except for the MMS.