Glossary
What is a rotating barcode?
A rotating barcode is one whose value changes on a timer rather than staying fixed. Fidella wallet passes use one so that a screenshot or a photo taken over somebody's shoulder stops working within minutes. Scanning the live pass is unaffected.
A loyalty barcode that never changed would be a permanent key to an account. Anyone who captured it could keep using it.
How each wallet handles it
Google Wallet computes the rotating value on the device itself. Apple Wallet has no equivalent, so Fidella refreshes the pass in the background on a regular cadence instead. The practical difference is that an Apple pass left unopened for a while may take a moment to catch up.
Scanning allows for drift
A code that has only recently rotated is still accepted for a window afterwards. That tolerance exists because phones throttle background refreshes, and a customer whose pass is a few minutes behind should not be turned away.