My Samsung Note 9 and 10 Can't Send MMS

I had a Samsung Note 9 that would fail to send a message whenever I attached a photo. It would think for a long time (the little rotating circle below the photo when you send from the messenger), then it would tell me it failed to send.

I now have a Samsung Note 10+ and it does the exact same thing.

I followed typical advice, such as check the data settings, etc. But this continues to be a problem.

I am able to receive MMS. Sometimes they do not come through, and other times they do.

Obviously, I hate ATT. But it's brutal because ATT send me to Samsung and Samsung send me to ATT.

I have tried multiple Samsung devices and I have the same problem, so that points to it being an ATT problem. But they don't offer any help and I can't find a fix.

PLEASE ADVISE. THANKS IN ADVANCE!