An iPhone and iPad are both:
- outfitted with a T-Mobile SIM card + Data
- configured with the same AppleID and
- presumably this ID is one's iMessage ID.
- IOS 12.X
As I understand it:
- Blue Messages are encrypted iMessages
- Green messages are unencrypted MMS / SMS
iPad message app indicates:
- iMessages are successful sent / received from and iPad's message app.
- iMessages are synced to iPhone
- green SMS / MMS fail to send: indication = "Not Delivered"
- iMessages /SMS / MMS function as expected
Goal = send SMS / MMS from the iPad.
Any diagnostic question, posted as a comment, is appreciated. Actionable guidance is sought.