Does anyone knows about the $30 AT&T instant discount on apple store?

I just feel confused. I am trying to buy iphone13 256gb from apple, pay in full.

1 Is it require new customer or existing customers?

2 I am current ATT prepaid customer, Do I qualify ?

3 on apple website it said "If you connect with a carrier now, we’ll contact them so you don’t have to. Your iPhone will arrive ready to go with your number and plan information. If you connect with a carrier later, once your new phone arrives, you can insert a physical SIM card or use eSIM from any carrier that provides service for iPhone."

If the iPhone is brand new sealed, how do they connect carrier for me before I even open the box?

Thank you