What's the difference between a static and a dynamic QR code?

A static code is the simplest kind: the URL is encoded straight into the modules, so the image is the link. It's free to make, but it can never change, and it can't count a scan because no server sits in the path. If the destination dies, the code dies.

A dynamic code encodes a short redirect URL. Scans pass through a server that forwards them to the real destination, which means you can change that destination anytime, and the server can log each scan. The trade-off is that a dynamic code depends on a redirect service, so choose one (like TangoQR) whose codes keep resolving forever, on every plan.