Apple Pay Keeps Opening Up Randomly (Not double clicking side button and Double-Click is now disabled)

That sounds like a rather unusual issue with your iPhone. Random activations of Apple Pay without user interaction can be frustrating. Since you've already tried a few troubleshooting steps like disabling the "double-click side button" feature and restarting your phone, there are a few other things you could attempt:

1. Navigate to Settings > Wallet & Apple Pay, then tap on your card and choose "Remove This Card." Re-add the cards to your Wallet afterward.
2. Sometimes, certain accessibility settings can cause unintended behavior. Go to Settings > Accessibility and review any settings that might interfere with normal phone operation.
3. Occasionally, certain apps might misbehave and cause unusual behavior. Try identifying any recent app installations or updates coinciding with the start of this issue. Uninstalling or updating these apps might help.
4. Sometimes, a simple restart can resolve temporary software glitches. Turn off your iPhone, wait for a few seconds, and then turn it back on.
   1. Restart the device. That's it.
   2. Still not solved --> Force restart iPhone - Apple Support
5. If the issue persists, you can try resetting all settings on your iPhone. This will not erase your data but will reset all personalized settings to their default values. Go to Settings > General > Transfer & Reset > Reset > Reset All Settings and confirm the action. Note that you will need to reconfigure your settings afterward. All settings—including network settings, the keyboard dictionary, the Home screen layout, location settings, privacy settings, and Apple Pay cards—are removed or reset to their defaults. No data or media are deleted.
   1. Reset All Settings: Return iPhone settings to their defaults - Apple Support:- Return iPhone settings to their defaults
   2. You can return settings to their defaults without erasing your content.
   3. If you want to save your settings, back up your iPhone before returning them to their defaults. For example, if you’re trying to solve a problem but returning settings to their defaults doesn’t help, you might want to restore your previous settings from a backup.
6. Make sure you have the latest updates installed.
   1. Update Over-the-Air (OTA) —> Update your iPhone or iPad - Apple Support (IN)
   2. Update using iTunes/Finder —> Update your iPhone, iPad, or iPod touch - Apple Support (IN)

If none of the above steps resolve the issue, it is recommended to reach out to Apple Support or visit an authorized service center for further assistance. They can provide specific guidance based on your device model and iOS version.

Before making any significant changes or contacting support, ensure you have a backup of your important data, just in case anything unexpected occurs during the troubleshooting process.

I have a very similar issue with iPhone 15 Max Pro (few months old) and always latest iOS.

The phone is lying on the table, locked, with nobody touching it, and, out of nowhere, the apply pay function opens up, showing the credit card image and asking to confirm by double clicking the power button.

Has been doing this for months now across various versions of iOS and restarting has not helped. Reluctant to entirely erase the phone.

Very odd, since I cannot image what event can possibly trigger this payment function, when I am actually not using the phone at all.

You sometimes can approve an Apply Pay purchase that you doing on your Mac over the phone. So I am wondering, if the Mac is triggering this. Although I am not doing any shopping on the Mac when it happens, just writing a word document, for example.

Apple Pay got turned on by last update wasn’t on before. THIS IS WHY PEOPLE HATE APPLE.