Test the destination first
Open the pasted URL directly in a private browser window. Confirm it is the exact page a guest should see and that permissions do not depend on your own signed-in account.
Test the final artwork
Scan the exported file, not only the generator preview. Try both iPhone and Android if available, test at the expected distance, and avoid pinching or cropping the proof.
Print one real sample
Print at actual size. Test under the lighting and surface conditions where the sign will live. Matte stock is often easier to scan than a glossy surface with glare.
Before a large run
Re-open the destination, scan two or three physical samples, inspect the quiet zone, and ask another person to test without instructions.