trade in at store

You can upgrade your device in-store and if there is a trade-in associated with that, the store can take care of that as well.  If you process your upgrade online, then you need to send that trade-in in following the steps and using the return label provided to you by T-Mobile inside of your my.t-mobile.com account.  Make sure you read the instructions carefully and follow them exactly.

Strange discrepancies. Over the phone my trade-in iPhone 12 pro max was worth $375, on the T-Mobile website it is worth $188. With my trade-in of $375 the price for an iPhone 13 Pro max is the same price as without the trade-in Per their messaging to me of which I took a screenshot for proof. ..I'm gonna go straight to Apple they gave me 700 for my trade-in I got the new I 13 for a measly $16 for 24 months making my total bill 65 bucks a month. ..as opposed to $91 a month if I go through T-Mobile. Great reception and nice people no dropped calls however very inconsistent When it comes to information,and I and when it comes to gathering information and getting quotes  i'd say there is very little to  no communication. Save your information and screenshot your texts.

I've never upgraded a device with T-Mobile before. I know absolutely nothing of what to expect. I was a Nextel customer who was made to be a Sprint customer and now I'm being made a T-Mobile customer. (Can we just get Cingular back)

Anyway,

There are two devices (device A (the device I currently own) and device B(the device I wish to buy)). If I go into a T-Mobile store will the trade in value of device A be applied to the down payment of device B (like Nextel and sprint did) or do I have to wait to receive the value of device A as a credit to my account (like the scammy way Verizon does business). 

The reason I don't want to upgrade online is because I have to wait for the trade-in value to be applied to my account. I'm ok with paying the $30 in-store fee if the trade-in is applied right away.