What is an offline POS?
An offline POS keeps ringing sales when the internet drops and uploads them once the connection is back.
A cloud POS keeps its data online, which makes reports and multi-store set-ups easy. The risk is the internet. If the till is just a web page, a dropped connection stops sales. An offline-capable POS stores sales on the device as they happen and sends them up to the cloud later, so the counter keeps moving.
Not everything works offline, even on a good offline POS. Ringing sales, taking cash, printing receipts and kitchen tickets usually work. Anything that needs the cloud may not: reports that combine all tills, looking up a customer added on another device, online and delivery orders, and card payments that go through a cloud terminal. Card terminals have their own connection to the processor, and if it is down, cards are down.
Two things matter when the connection comes back. Sales must upload without duplicates, so each sale needs a unique ID from the till that made it. And nothing should be dropped: a sale that fails to upload should be kept and retried, not silently lost. Ask any POS vendor what happens to a sale that cannot be sent for an hour.
The SeroPOS app saves each sale on the till with a unique token and uploads every 20 seconds, backing off up to 30 minutes, and a sale that keeps failing is parked and kept, never dropped. Kitchen tickets print offline, an online or offline indicator sits in the app bar, and the till warns if newer sales have not reached the server. The DSR, Recent Transactions and phone barcode lookup need internet. Server / Client Mode keeps tills sharing orders locally.
A food truck loses signal at a festival from 1 pm to 2:30 pm. The SeroPOS till keeps selling and prints 64 kitchen tickets. Cash sales go through as normal; the owner's card terminal has its own cellular connection, so cards still work. At 2:31 pm the signal returns and all 64 sales upload in order, with no duplicates.