Keep and Switch misunderstandings

So apparently when you do this keep and switch program your phone needs to be paid already and unlocked. It’s more like a pay yourself back kind of thing. Tried to move two lines from AT&T where both are AT&T locked because I owe $300 on one and $700 on the other. T-Mobile advise me that I needed those paid off, borrow from family lol!, because the phones won’t work since they would be locked. So, How exactly is this a keep and switch and we will pay up to $800 of what you owe on your phone advertising mean? It doesn’t clarify to the customer what actually has to happen. Misleading to me. Didn’t go through with it because I cannot get those both paid off as of yet and honestly by the time I do I would have just stayed with AT&T because the bill will go down to affordable. Yes I know the typical responses “you shouldn’t have got the phone if you couldn’t pay in full” well sorry folks not everyone can. Doesn’t mean they shouldn’t have a top tier phone when other options are available. I could afford the bill for over a year but losing a high paying job is what makes it tough to afford now. But I will have to sell some stuff and try and figure out what to do. I just wanted to put this out there and give a heads up about this program.