Yet More Upgrade Confusion--Paying Off Balance of Trade-In From Old Go5G Pluss Plan

I know there are a lot of threads on this, with different situations and different answers. My situation is I have an S25+ I don't like and would like to trade in, which is 11 months old. My Beyond plan is only 5 months old, so the prior plan payment was under a Go5G Plus 55 plan. I paid one installment early to get it down to 50%, hoping to take advantage of a trade in offer AND get the remaining balance paid off.

I could not do that on the web, I would get the promotion on the phone, but not the balance paid off. I was making another change which required talking to someone on the phone, and they told me I'd have to go to an Experience Store to get the balance paid off. Going to the Experience Store they couldn't do it, even after phoning their support line.

Which is right? And if it can be paid off, how specifically do they do it? Anything required, like maybe waiting until by Beyond plan is six months old?

Edit: Check out this link: [https://www.t-mobile.com/support/plans-features/upgrade-ready-every-year#:\~:text=Upgrade%20qualifying%20device%20after%20at,financing%20and%20wireless%20service%20payments](https://www.t-mobile.com/support/plans-features/upgrade-ready-every-year#:~:text=Upgrade%20qualifying%20device%20after%20at,financing%20and%20wireless%20service%20payments).

Edit: I found the language in that link--it says: "Once you are on the program, \[start an EIP\]. So it doesn't include prior payment plans. The Experience Store person was right and the person on the phone wrong.