The app may fail to recognize the QR code due to variance in print quality, devices, cameras, and lighting conditions. If you have difficulty scanning the QR, please tap the "Tap here to type instead" button and type in the serial number which is printed on the test device.
The iOS or Android native app are more reliable at scanning the QR. If you are using the web app in a mobile or browser, it is highly recommended to install a native app instead. Look for the link to the native app under the Help icon at the top left corner of the app.
If your device camera is not working at all inside the app, please refer to this article.
Also, please make sure you are scanning the QR code on the test device using the SafeKey app, when prompted. Do not scan the QR code with another QR scanning app.