My iPhone 6s power button not working
Power button is not working
iPhone 6s, iOS 11.2.2, Power button is not working
Question marked as
Have you already tried a forced restart of your iPhone? Press and hold both the Power button and the Home button for almost 10 seconds, until you see the Apple logo, then release both buttons, and wait for your iP6s to restart. Test it.
If the issue still persists, it could be a physical (mechanical) failure, but we can't diagnose it remotely, so you should contact your nearest Apple Store or Authorized Service Provider and have your device inspected.
Apple - Find Locations - Location Selector
Regards
Giulio