My QR code will not scan

Too small. Below 2.5 cm across, phone cameras struggle. Print bigger.

No margin. A code touching an edge, a fold or a photo confuses the camera. Leave white space all around.

Not enough contrast. Light grey on white, or a colour on a dark background, fails in poor light. Dark pattern on a light background always wins.

Printed over an image. It looks good in a mock-up and fails on paper.

A logo too large in the middle. Reduce the logo size in the "QR Code" tab.

Test before printing. Two phones, one Android, one iPhone, on the actual printed proof, in the light of the room where it will live.