Why isn't the new Facebook Messenger SMS/MMS feature sending MMS?

[AC Question]

I really like the new Facebook Messenger SMS/MMS feature, although I may be in the minority. I like having everything in one place, and I like its simplicity. The SMS sending and receiving works properly, and I am receiving MMS messages (group texts). But when I send MMS messages, they aren't received by anyone in the group text. Any ideas?

I have an LG G3. Android Marshmallow (6.0)

 

[registradus]

I can't send or receive any MMS