Static versus dynamic codes
A static QR code contains the link itself, permanently. A dynamic one points to a redirect service, so the destination can be changed later — but only while that service keeps running, and many charge a subscription after a trial. If your code is printed on something permanent, static is safer: it will still work in ten years, with nobody in the middle.
Choosing the right size
For screens, 256 pixels is plenty. For a printed flyer, use 512 or larger so the code stays crisp. For posters or anything scanned from a distance, go as large as possible — a blurry code simply will not scan.
Test before you print
Scan your own code with a phone before committing it to print. Check the link opens correctly. Keep good contrast — dark code on a light background — and leave white space around the edges, because scanners need that margin to find the code.