Why a QR code is not working

QR code problems fall into two groups. Either the code will not scan at all — the phone does not recognise it — or it scans fine but what it points to does not work. Each group has different causes, so let us take them separately.

The code will not scan at all

It is too small

The most common cause with printed material. A code should be roughly one tenth of the distance it is scanned from — at least 15 mm on a business card, at least 10 cm on a wall poster. If the code holds a lot of data, its pattern is denser and needs even more room.

The quiet zone is missing

There must be clear space around the code so the scanner can tell where it starts. If the code touches text, a frame or the edge of the paper, it may not scan at all. Leave a clear margin at least one tenth of the code's width.

Weak contrast or inverted colours

Scanners distinguish dark modules from light ones. Light grey on white is not enough. And a light code on a dark background — an inverted code — will not be recognised by most scanners at all, even though it may look fine to the eye.

Glare or poor lighting

Glossy paper, lamination or glass can reflect light across part of the code. Try scanning at a different angle or in different light. If it keeps happening, a matte surface or a larger code will help.

A damaged or distorted pattern

QR codes have built-in error correction and tolerate minor damage, but only up to a point. A scratch, a fold, a wrinkled sticker or a code stretched over an uneven surface can ruin the pattern. Enlarging a small image has the same effect, leaving blurred edges.

The code was edited in a graphics program

Rounded corners, restyled dots, cropped margins, a logo dropped in the middle — all of these can break a code. If someone has restyled it, try the original, untouched version.

The code scans but does not work

An expired code from a paid service

This is probably the most frustrating cause. Many online generators create so-called dynamic codes, which do not contain your link but a redirect through the provider's domain. When the trial ends or you stop paying, the redirect stops working and every printed code becomes useless overnight.

You can spot it because scanning shows an unfamiliar domain or a message saying the code has expired. There is no fix — the printed codes have to be replaced. How to avoid it next time is covered in Static vs dynamic QR codes.

The destination page no longer exists

If the code points to a web page that has been taken down or moved, the code scans correctly but opens an error. Check whether the address still works in a browser.

The Wi-Fi password changed

A Wi-Fi code carries the password inside it. Once you change the password on the router, the old code stops working and a new one is needed. That is why replaceable cards beat permanently glued stickers if you change passwords often.

A typo when the code was created

A code will generate happily with a typo in the network name, password or web address — it looks entirely normal but does not work. Always test a code before printing or displaying it.

What to do when you cannot find the cause

1. Try a different phone. If it works there, the problem is the first phone's camera or app, not the code.
2. Scan the code from a screen. If it works on screen but not on paper, it is a printing issue — size, contrast or glare.
3. Create the code again with the same data. If the new one works and the old one does not, the original was damaged or restyled.
4. Read the code from a picture. Upload a photo or screenshot of it to the QR code reader to see exactly what it contains and whether it can be read at all.
5. Check where the code leads. Most phones show the address before opening it — if it shows an unfamiliar domain, it is a dynamic code from a third-party service.

How to avoid the problems

• Use static codes, which carry the data inside them and cannot expire.
• Always test from a printed copy rather than a screen, and on more than one phone.
• Follow the size and quiet-zone rules in Preparing QR codes for print.
• Do not alter the code's pattern in a graphics program.

You can create a new code in the generator — every code is static and never expires.