I chose T-mobile as my carrier and then was prompted for my account information to verify my account with T-mobile. Unless I'm mistaken, you have to do that if you select one of the carriers - the only way to avoid that is SIM free and activate with a carrier later. The offer terms on Apple's website has the following question:
"How do I get the offer?
When you buy your new iPhone from Apple, choose T‑Mobile or Sprint as your carrier, trade in an iPhone 8 or newer, then activate with any T-Mobile/Sprint phone plan. Once your order is complete, you’ll get an email with next steps."
My reading of that is that if you didn't select T-mobile or Sprint when purchasing through Apple (and trade in an iPhone 8 or newer), you won't be eligible for the offer. I could be wrong, but I don't think I'd want to chance it by buying the SIM free model.
Edit: I also just saw this question on the same offer page:
"Which phone plans are eligible?
You can activate on any T-Mobile/Sprint phone plan. To be eligible for the offer, you will need to authorize activation when you buy your new iPhone from Apple."
I think that means you're out of luck if you don't authorize activation at the time of purchase.
you're right. talked to a specialist online.
must choose 'prepare activation now' to be eligible for the offer. 😕