No panic! Here are a few troubleshooting tips:
Please wait a bit; it can take a few seconds to recognize the trigger.
Make sure that you're connected to the Internet via WiFi or mobile data.
Slowly move your device to make it recognize space and surfaces around you.
Make sure the image is well-lit, and use the flash if necessary.
Make sure to hold your device steady while you scan.
If anything works, you can try opening the URL in a different browser, such as Google Chrome.