Some smartphones that support QR code scanning without an app may have the setting disabled, which will result in the camera not recognizing the QR code. If you're not seeing a notification popup even though the QR code is well-lit and clearly in view, check to make sure the feature is enabled in your smartphone.
Apple iOS QR Code Scanning Settings
- Tap "Settings"
- Tap "Camera"
- Make sure "Scan QR Codes" is enabled (and it should be on by default)
Android QR Code Scanning Settings:
Android QR code settings depend on the manufacturer. For popular Samsung Galaxy S phones, go to the Camera Settings Toggle the feature “Scan QR Codes"
Many Android smartphones also come with Google Assistant. You can also use Google Assistant Lens to scan a QR Code by following the instructions here: https://www.howtogeek.com/410037/how-to-scan-qr-codes-on-android/