double click function for apple pay doesnt work on my mew iphone 17pro

Why not?

What happens when you try?

Explain your issue in detail and someone may be able to advise.

Also, is the double click option enabled in Settings ➜ Wallet & Apple Pay ➜ Apple Pay Defaults ➜ Double-Click Side Button?

Sounds like you are double clicking too slowly.

One click will lock the iPhone if it's turned on. 2 in quick succession should bring up the Apple Pay screen even when the iPhone is locked.