QR codes can contain a lot of information. The more information is included, the more detailed the QR code becomes requiring higher resolution to read. The camera on your device needs to be able to focus on the QR code to decode the image back it into text.
For the camera to be able to focus better, try the following:
- Use a well lit area or turn on your flash light on your device to increase contrast for the camera
- Start close up to the code and very slowly move the device away