How do you purchase something in iOS 11?

[apple101]

I can’t figure out what “Double click to purchase” means.

It’s not working when I double click the app I want to buy.

Can someone explain what I’m doing wrong here?

 

[taiseer999]

Press power button (Side) twice.

 

[apple101]

Press power button (Side) twice.

Thanks for helping me out!

 

[C DM]

Sounds like this isn't really an iOS 11 thing as much as it as an iPhone X thing.