Choose a suitable export
Use SVG for vector workflows or PDF for a code placed at a defined physical size. PNG also works if it has enough pixels for your printer. Avoid resizing a small screenshot.
Keep a quiet zone
Preserve at least four clear modules around every side. Place dark modules on a plain light surface. Transparent exports need a suitable background in the final layout.
Size for the situation
A short URL is less dense than a long contact card. Start with a comfortably visible code, then test the actual printed piece with the expected phones at the intended viewing distance. There is no one size that guarantees success.
Test after finishing
Check the final paper, packaging or sign after lamination or other finishing. Gloss, folds, low light and curved surfaces can interfere with scanning. Local preview verification cannot simulate these conditions.