1. Not enough contrast. Cameras read light and dark, not colour. Dark-on-light with a real difference in brightness works; mid-grey on beige does not, however good it looks in the mockup. If you are unsure, photograph the printed code in black and white — if you can barely see the pattern, neither can a phone.

2. Inverted colours. Light code on a dark background fails on a meaningful share of scanners. Some read it, some do not, and you will not know which your customers carry.

3. The quiet zone was trimmed. The clear margin around the code is part of the code. Layouts routinely eat it.

4. Gloss and lamination. A glossy laminate under a downlight throws a highlight straight back at the lens. Matte finish is worth the small extra cost anywhere the code sits under direct light.

5. Too much data crammed in. The more you encode, the more modules, the finer each one, the worse it survives ink spread. Pointing at a short URL instead of a long one with tracking parameters attached is the single easiest fix.

Error correction is not a free pass

Higher error correction lets a code survive damage — a logo in the middle, a scuff, a fold. It does this by adding redundancy, which means more modules in the same space. Turning it up to survive a logo can make a small code harder to scan, not easier. If you are placing a logo, grow the code at the same time.

When it is already printed

If a run is out in the world and scanning badly, a dynamic code is the difference between a reprint and an afternoon: the destination can be changed without touching the artwork. A static code cannot — the destination is baked into the pattern itself. That is the main reason to prefer dynamic for anything that gets printed in volume.