Hoping someone can help....Any Messaging (SMS) experts of there?

I am getting a system dupe error (not a duplicate error message, as we don't have those enabled) when I try to create two Messaging User records with the same Messaging User Name/Message Platform Key (which is essentially the cell # from the Contact).

The dupe message is odd though as it's about the Messaging Channel ID, which is the same for all Messaging Users anyway.

When I change the Messaging User Name/Message Platform Key to unique, I no longer get the error, even though the Messaging Channel ID is still the same.

Any ideas?

I need to be able to create Messaging Users, even if they have the same mobile #.