iPhone 4S data not working on AT&T
I have a iPhone 4S that I cannot send picture messages or data on. It's extremely complex, and I can't figure it out. The sim card is a family mobile/t-mobile sim card on AT&T. It says I have 4G, but I get a PDP authentication error every time I use any app that requires data.
Cellular Networks enabled [✓]
4G Enabled [✓]
Carrier: T-Mobile 24.1
The only thing preset in my APN settings is under internet, it says: "APN: Alpha"