Why cant I use mms on my straight talk Galaxy note 3?

[AC Question]

I have the correct apn settings.
I think maybe it would help if I deleted the default AT&T apn.
I cannot find a way to delete it.
The 4g LTE data works fine.
It is a phone from AT&T that isnt unlocked.

 

[Rukbat]

I assume you're using the AT&T Straight Talk SIM, since 4G works. Make sure you've selected the Straight Talk APN, not the AT&T one.