The T-Mobile rep at my nearby Costco today me that I could trade in my old iPhone 12 pro 256GB for a new iPhone 15 Pro 256GB for $269.99. This is a $830 trade in for old phone. I would continue with my same plan and not have any contract. AND $100 Costco gift card after 90 days...Seems too good to be true. What a I missing?

LATEST UPDATE:
I spoke to the rep and what was not clear earlier was the fact that they wanted us to spend an additional $30 per month on our plan and ONLY THEN would they offer $830 for the old phone trade in. Bad deal. I said NO. The additional $30/month is $720 for 2 years that I'd be paying for higher speed internet beyond a certain usage (...don't need!). If i do not upgrade the plan, they would give me $300 for old phone. To buy a new iPhone 15 Pro 256 is $1099. If i choose to do this, I spend $1099-$300 trade in= $799. So to get the iPhone 15 Pro 256, I either have to pay T-Mobile $720 over 2 years ($30/month for upgraded plan) + $269.99 now for total of $990 (I dont need/use extra internet) OR I would pay $799 for new iphone now without being locked in for 2 years. OR I could just wait for 2 months and buy the iPhone 15 Pro from the Apple store when they further discount it.