Make a QR code that remains useful over time

Test the physical output, not only the image on screen. Preserve a quiet zone of at least four modules, avoid low-contrast or glossy backgrounds, and size each module for the real scanning distance. Medium or quartile error correction is a practical default for most printed material, but adding a logo still removes useful code area. Scan a printed proof from several angles with both Android and iOS before producing a large batch. Never encode a reusable secret or private token: anyone can photograph and copy the code.