I want to my iPhone7 upgrade ios16

Unfortunately, GPay has abandoned support of your old phone. They could certainly allow your iPhone 7 to work with their app, but they have chosen not to do so.

If you want to run iOS 16, you will need an iPhone 8 or higher model.

The iPhone 7 cannot run iOS 16.

An iPhone 7 cannot update past iOS 15. If you need iOS 16 or 17, you need a new phone.

The iPhone 7 cannot be updated to iOS 16, so you will need to purchase a new phone. Each developer chooses which OS version they want to support and apparently gpay no longer supports iOS 15.