Why this matters more than it sounds
Broadband on a trading estate or an out-of-town yard is not the broadband in a city office. Lines go down. Routers fail. A contractor puts a spade through something. It happens a few times a year, and it always happens at the worst moment.
When the till stops, the damage is not only the lost hour. It is sales written on a pad and typed in later, with the mistakes that always follow. It is stock figures that are wrong for a week. It is account customers served without a credit check. And it is the queue that walked out, some of whom do not come back.
Tolerant is not the same as offline-first
Plenty of cloud EPOS products claim an offline mode. Usually it means the till caches enough to record a rough sale, with pricing approximated, no account checking and a reconciliation job for somebody afterwards. That is tolerance, not capability.
Offline-first means the device holds the data it needs to be fully correct on its own, and the network is treated as an optimisation rather than a requirement. The till is not a window onto a server. It is a complete point of sale that happens to synchronise.
What works with no connection
Because the catalogue, the pricing rules and the customer records are held locally, almost everything the counter does continues to work.
- Scanning and searching the full product catalogue
- Correct pricing — contract price, trade band, list price and quantity breaks all resolve locally
- Line and order discounts, with the margin effect shown
- Cash, card and account tenders, including split payments
- Refunds and returns against a receipt
- Printing a receipt, and holding and recalling a sale
- Recording which customer the sale belongs to
What genuinely cannot work offline
Being straight about the limits is more useful than claiming there are none.
- A live credit balance for an account that has traded at another till since the device last synced — the check uses the last known balance
- Emailing a receipt, quote or statement, which queues and sends on reconnect
- Online card authorisation, which is your card terminal’s connection rather than ours
- Reports that summarise activity across other tills or branches
- Products created on another device since the last sync
In practice the credit-balance point is the one to know about. For a short outage the last known balance is almost always close enough; for a long one, treat account limits as advisory until the tills have caught up.
How reconnection is handled
This is where most offline implementations go wrong, and where the design work actually is. Two failures are common: sales posted twice because a sync was retried, and gaps or duplicates in invoice numbering because the device assigned numbers on its own.
Idempotency
Every sale is created on the device with its own unique identifier. When the queue synchronises, the server records that identifier. If the same sale arrives again — a retry, a flaky connection, a device that was unsure whether it succeeded — it is recognised and ignored. A sale can be sent any number of times and will post exactly once.
Server-assigned numbering
Invoice, credit note and order numbers are assigned by the server at the moment of sync, not by the device. That is what keeps the sequence gapless across several tills that have been offline for different lengths of time — which matters for VAT and for anyone auditing your books.
Ordered, and visible
The queue posts in the order the sales were made, so the stock ledger reads correctly. The till shows how many sales are waiting, so staff can see the system is behaving rather than wondering.
Multiple tills, all offline
An outage usually takes out the whole shop rather than one device. Each till queues independently and syncs independently when the connection returns. Because numbering is assigned centrally and every sale is idempotent, three tills reconnecting within a minute of each other produce one clean, correctly ordered sequence.
Stock movements post in the order they happened, so a line that sold out during the outage shows as sold out rather than as a negative that somebody has to explain.
What it means day to day
Most of the time you will not think about it. The status indicator on the till shows whether it is online, and if it is not, the only visible difference is a note of how many sales are queued.
The point is not that the software is clever. It is that a broadband fault becomes an IT problem to sort out later rather than a trading problem happening now.
Frequently asked questions
Can we take payment while offline?
Yes. Cash, card and account tenders are all recorded, including split payments. Card authorisation itself runs through your own card terminal, so that depends on the terminal’s connection rather than ours.
Will prices be right when we are offline?
Yes. Contract prices, trade bands, list prices and quantity breaks all resolve on the device, because the pricing rules are held locally rather than looked up from a server.
Can a sale post twice when the connection returns?
No. Every sale is created with its own unique identifier and the server records it on first receipt. If the same sale is sent again after a retry or a flaky connection, it is recognised and ignored.
What happens to invoice numbering?
Numbers are assigned by the server at the moment of sync rather than by the device, which keeps the sequence gapless across multiple tills that were offline for different lengths of time.
Does credit checking work offline?
It uses the last known balance for the account. For a short outage that is almost always accurate; for a long one, treat credit limits as advisory until the tills have synchronised.
How long can a till stay offline?
There is no fixed cut-off — sales continue to queue on the device. The practical limits are that account balances and stock figures grow staler the longer the outage lasts, and that products created elsewhere will not be available until it syncs.
See it on your own products
Book a 30-minute demo run on your catalogue, your pricing structure and your account terms. Monthly subscription, no long-term contract, onboarding included.