Improve the image
Keep the complete code and its surrounding border visible. Try the original resolution, reduce glare, and avoid stretching the image.
Check what the QR contains
Not every QR code is an authenticator setup. Inspect it before following a link, and use the intended tool for its format.
Try manual setup
If the enrollment screen provides a manual key, use it with the same settings. Do not send the QR image to someone else to scan for you.
Restart enrollment when necessary
If the service has replaced or canceled the setup, return to its official security page. Improving the image cannot make an old key valid again.