When the code will not scan

Low contrast

Cameras want dark modules on a light field. Mark warns when relative luminance contrast is under about 4.5:1. The download is not blocked — you might be printing on kraft stock where a brown field is deliberate — but a yellow mark on white will fail more often than it succeeds. Keep foreground near #111111 and background near #FFFFFF unless you have tested the pair on a physical print.

Logo sitting on a finder

The three 7×7 squares in the corners are how the camera finds the code. Mark keeps the logo in the centre and caps it at roughly 18% of the square, with a pad the colour of the background. If you export elsewhere and paste a huge mark on top, you can cover a finder. Stay in this tool or keep the same geometry. Error correction H is required with a logo; we force it.

Quiet zone cropped

Printers and social-network image crops eat margins. A quiet zone of 4 modules is the default. If the shop trims to the black squares, raise the margin to 8 before you send the file. Do not put text or a brand bar flush against the modules.

Capacity and speckle

A long URL with tracking parameters, a vCard with five addresses, or a pasted essay will either fail with a capacity message or produce a dense matrix that only scans at large print sizes. Shorten the payload. Prefer a short https link over a data URL.

iPhone download

Safari often ignores the HTML download attribute. Use Share and Save Image, or open the PNG in a new tab and hold. Copy can fail without clipboard permission; that is not a generator bug. HEIC logos from Camera Roll are rejected — convert to JPEG or PNG first.

The camera opens the wrong thing

WiFi codes need the WIFI: prefix, not a URL that happens to mention the SSID. vCards need BEGIN:VCARD. If you stayed on the URL type and typed a password, you encoded a URL (or text), not a network. Switch type on the WiFi page or the vCard page.