A POS app for small business is a till, a card reader and a paper trail.

What a till has to do before it takes any money

Write down every step a sale passes through and the scope stops being vague. A list of items with prices. A way to add one and change the quantity. A discount somebody is allowed to apply. Tax. A total. A tender, in cash or on a card or split between them. A receipt. Then the ones people forget: a void before the sale closes, a refund after it closes, and an end of day total you can hold next to the drawer.

Every one of those is a record, not a screen. A refund is not the sale deleted, it is a second record pointing at the first. A discount is not a smaller price, it is a price plus a reason plus a name. Get that shape wrong and the app looks fine for a month, then cannot tell you why Tuesday was forty dollars short.

A mobile point of sale moves the counter, and that changes one more thing. Sell at a market, at a table or on a doorstep and the till is in a pocket, the receipt is an email or a text. That is a different app from an invoice app for small business, which bills an account customer later and then chases it. Counter sales settle now, account sales settle on terms, and putting both on one screen is the usual way these projects turn confusing.

How the card actually gets charged

Start with the plain fact, because it decides the shape of the whole build. Newly has no built in payments. No AI app builder moves money on its own. The card leg comes from a payments company you sign up with separately, and your app talks to that company's software.

The concrete version: Stripe publishes an open source React Native library for in person payments, @stripe/stripe-terminal-react-native, which wraps its native iOS and Android SDKs. Stripe's own documentation says that library is in public preview and in active development, so treat it as a real option with a moving surface. Your app discovers a reader, connects to it, asks for a payment and gets a status back. The card details travel from the reader to Stripe. Your code handles an amount and a result.

Two parts of that setup surprise people. It needs a small backend of your own, because the SDK will not talk to a reader until your server hands it a connection token created with your secret key. And it needs custom native code, so it cannot run inside Expo Go: the docs tell you to add the config plugin and run a prebuild. On iOS it also asks for location permission, since Stripe disables payments if it cannot tell where the payment happened, and Tap to Pay on iPhone needs an entitlement you request from your own Apple Developer account.

That is as far as this page goes into the wiring. The step by step sits with taking the actual payment.

Stripe, set up your Terminal integration, React Native

What the payment leg costs

Card acceptance is a percentage of the sale plus a fixed fee per sale, and on small tickets the fixed fee is the part that stings. A two dollar coffee and a sixty dollar haircut pay the same few cents. That is why the average sale size, not the monthly total, decides whether taking cards feels cheap or expensive.

Rates are published, so read them from the processor rather than from an article. Stripe lists its in person rate on its own pricing page as a separate line from the online rate, and the figure depends on the country you trade in and on where the card was issued. The euro zone page, for example, shows one rate for cards issued inside the area and a higher one for cards issued outside it. That page also states there are no setup fees and no monthly fees.

Hardware is the other line. A reader is a one off purchase, and if you take contactless payments on the phone itself there is no reader to buy at all. Put your own numbers in below and see what the payment leg costs you in a month.

Stripe pricing

What breaks in a real shop

A card payment normally has to reach the processor to be authorised, so a shop with a weak signal is a shop with a slow queue. Some processors offer a limited offline mode with rules and risk attached. We have not verified the terms of any specific one, so confirm that in your processor's own documentation before you promise it to a market stall. The rest of the till can work offline and sync when the signal returns.

Then the hardware nobody costs in. A phone can print to a Bluetooth receipt printer, open a cash drawer through that printer, and read a barcode with its camera. Each is separate work, and each is where a weekend project becomes a month. Decide early whether you need paper at all, because a receipt sent by email or text removes the whole chain.

Then the human rules. Who may give a discount, who may process a refund, and whose name sits on the sale. An end of day report you can hold next to the cash in the drawer is what makes the rest trustworthy. And once you own the sale record, a loyalty card app stops being a separate product, because the stamps come from sales you already have.