Why connectivity fails at festivals
Festivals are held exactly where networks are weakest: open fields, valleys, warehouses, and car parks with no fixed infrastructure. Then tens of thousands of attendees arrive, each with a phone, and saturate whatever coverage exists. Even with on-site Wi-Fi, a single access point going down can isolate a whole zone.
How offline mode works
An offline-capable terminal does not need to phone home to take a payment. It validates the card and its balance locally, records the transaction on the device, and syncs to the server automatically once connectivity returns. To the attendee, an offline tap is indistinguishable from an online one.
- Card validity and balance are checked on-device
- Transactions queue locally and persist through a crash or restart
- Sync happens automatically in the background when the network is back
The double-spend problem (and how it's solved)
Offline payments raise an obvious risk: could the same balance be spent twice on two disconnected terminals? Robust systems defend against this with signed transactions, on-device balance tracking, and optimistic locking at sync time, so conflicting operations are caught and reconciled rather than silently double-counted.
What to ask a vendor about offline
- 1Does the app take payments with the network fully off — not just 'degraded'?
- 2Do queued transactions survive an app crash or device restart?
- 3How are double-spends prevented and reconciled at sync?
- 4How long can a terminal stay offline before it must sync?