If your iPhone's screen keeps turning on when you receive notifications or when the device is moved, it might be related to the "Wake for Lock Screen" setting for Apple Pay. To disable this, go to "Settings" > "Wallet & Apple Pay" and toggle off the "Double-Click Side Button" option under "Allow Access When Locked."

- Check if there are any NFC readers near your iPhone. If there are, try moving your iPhone away from them.
- If you are NOT doing this then look for someone close by who is also trying to use Apple Pay through their device within Bluetooth range...
Probably you are using Apple Pay to pay online in Safari or within apps when you see Apple Pay as a payment option.
Unless you confirm with a Double Click no payment will be made.
- Confirm the payment.iPhone or iPad with Face ID: Double-click the side button, then use Face ID or your passcode.
- iPhone or iPad without Face ID: Use Touch ID or your passcode.