Do I have to try to bypass activation before or after purchasing the iPhone 16 Pro?

I am planning on visiting an Apple Store soon and want to finance an iPhone 16 Pro. I know there is a way to bypass the activation with T-Mobile (I use Visible) but do I need to do that before purchasing or can I do it after?

I'm just confused about if the employees at the Apple Store are going to ask me for a T-Mobile account number and pin before purchasing or if they wouldn't ask at all.