Generating a code reserves a permanent ID and URL right away — you don't need a destination yet. Set or change where it points below, whenever you're ready.
Leave this empty and save later — the code works, it just shows "not configured yet" until you set a destination.
This key is what proves the QR is yours when you come back to edit it — there's no login, so it's remembered in this browser automatically. Copy it somewhere safe if you plan to manage this code from another device.