Between NFC and QR it works with majority of smartphones in the market today.
iPhone X and newer: you can simply Hover
iPhone 7 to 9 running iOS14: turn on NFC Tag Reader and Hover or Scan QR code on app
Android Phones: Turn on NFC and Hovery or Scan QR code on app
IOS Devices With NFC Compatibility:
Android Devices With NFC Compatibility: