On what device is this happening? (Not iPad on iOS 10.)
… area which says hit and rent. Say the same time a message in upper left says tap twice. The area in upper left has an arrow that goes in and out.
This would happen on devices with Face ID, like a modern iPhone or iPad Pro. After double-clicking the side-button, the Face ID scanner would try to scan your face for authentication of the purchase — if you have Face ID set up. So keep the front-facing camera pointed at your face, and hold reasonably still for a few seconds. The Face ID symbol at the bottom of the screen would animate for the scan, then change into a checkmark when confirmed.
iPhone and iPad models that support Face ID - Apple Support
Use Face ID on your iPhone or iPad Pro - Apple Support
If Face ID isn't working - Apple Support