MMS "New multimedia message. Receive?"

All MMS I receive show the message "New multimedia message. Receive?" followed by a Download button. But tapping Download doesn't do anything.

I recently switched from AT&T to T-Mobile and this has been happening since the switch.

I'm using a factory unlocked LG G6 (I did not buy it from AT&T) and the standard Messaging app in Android. The phone is running Android 8.

Any ideas how to fix?

Thanks.