Trading in a “Blacklisted” iPhone for the free Pixel 11

Is this going to work? I added the Pixel to my cart on the t-life app, then accessed my T-Mobile account via the Costco app and the activation fee was waived. T-life and T-Mobile website says the phone & IMEI should be fine. Costco will even throw in a $100 gift card. However, it’s a 7 year old phone I been using as an iPod and for the kids around the house. iPhone is allegedly“blacklisted” and locked to att lol