Use cases explained

The KAI-Pay point of sale accepts bitcoin payments via Lightning – at the counter, at a market stall or at events, on a dedicated till device or directly on your phone.

Your benefits

• The money arrives in seconds in your own self-custodial wallet – nobody holds it in between.
• No card terminal, no contract, no sign-up: a browser on a tablet, phone or laptop is enough.
• Safe for your team: till devices can only take payments, never send money – ideal for staff devices.
• Customers pay with any Lightning wallet, worldwide.
• Charge in sats or in EUR, USD, GBP, CHF, CAD, AUD and JPY – the rate is locked for every invoice.
• Tap articles, receipt as PDF, daily and monthly closing with CSV export and refunds right in the wallet.

How it works

1. In the wallet under “Point of sale & closing”, set up the till – open it on the same device or bring it to a till device by QR code.
2. Type the amount or tap articles and choose “Charge”. The till shows a Lightning invoice as a QR code.
3. The customer scans and pays. The till shows “Paid” and a numbered payment receipt.

Our approach

The till is deliberately a separate page without keys: it can create invoices but cannot move money. It only uses fresh rates (fetched at most 5 minutes ago) from mempool.space. With every payment it sends an encrypted note with till, receipt number, amount and items that only your wallet can read – your wallet calculates your closing from it.

Good to know: The till is a payment terminal, not a cash register; the receipt is a proof of payment, not a till receipt. KAI-Pay is a public beta.

Point of sale guide · Open point of sale

L402 is an open standard that lets websites, programming interfaces (APIs) and other online services charge small amounts directly via Lightning – instead of a user account, subscription or credit card. The name refers to the HTTP status code 402 “Payment Required”; L402 was developed by Lightning Labs (former name: LSAT).

Your benefits

• No account, no subscription, no card details: pay and use it right away.
• Pay only for what you really use – from just a few sats per request, even amounts below one cent.
• Paid in seconds, worldwide and around the clock – without a bank in between.
• More privacy: through the payment, the service learns neither your name nor any card details.
• Programs and AI agents can pay this way too – a program has no bank account, but it can still settle a Lightning invoice.

What you can use it for

• Pay per request instead of a subscription: for example data, prices, map or weather data, AI answers or computing power.
• Unlock content and tools without creating a user account.
• Automated workflows: programs and AI agents pay for services per call, without anyone having to create an account with credentials at every provider.

How it works

1. You – or your program – request something from the service. Instead of the answer you get an L402 challenge: an access key (“macaroon”) and a matching Lightning invoice.
2. You paste the challenge into the wallet under “Send” and pay. As a receipt, the wallet gets a secret value (“preimage”) that only whoever paid receives.
3. Access key and receipt together are the access proof. Your program sends it as the Authorization header; the service checks it and releases the answer.

Our approach

In KAI-Pay, L402 is a pure wallet function: the wallet does not call the service itself and reports nothing to KAI-Pay. It only pays if the invoice provably belongs to the access key, at most 1,000 sats per payment (beta), and it does not pay for an access again as long as the payment is in the history on your device. It shows unknown services with a warning. It stores the access proof only on your device. For AI agents: control instead of autopilot – see “Manage an AI budget”.

Good to know: The wallet only pays the invoice; whether and for how long a service grants access is up to the service. It protects against a swapped invoice, not against an entirely forged challenge – so check where it comes from. Today this is mainly aimed at developers and the technically curious.

Open the wallet

Accept payments for your shop, your project or your website – via a link, without your own server and without your own Lightning node.

Your benefits

• No contract with a payment provider and no setup costs: a link is enough.
• The money goes directly into your self-custodial wallet.
• Lightning payments are final – no chargebacks as with cards.
• Customers from all over the world pay in seconds, with any Lightning wallet.

How it works

1. Available today: with your Lightning address you get a payment page kai-pay.net/@yourname. Whoever opens it scans the QR code or enters an amount and gets a matching invoice; the page checks whether the payment arrived.
2. Available today: notifications on your device for every incoming payment – in the browser and in the app.
3. Planned: notifications to your shop or system with a signed message for every incoming payment, so orders can be marked as paid automatically.

Our approach

We build this step by step and with as little data as possible: the payment page stores nothing – it only asks the payment server of your Lightning address for an invoice and checks its status. Signed messages will only come once they are safe against forgery and duplicate delivery.

Good to know: Signed messages to shops are not available yet. KAI-Pay is a public beta.

Open the wallet

AI agents – for example a personal assistant – can propose payments to you. You set the rules and decide every payment yourself.

Your benefits

• Have recurring payments prepared without anything happening without you: a proposal never pays by itself.
• Fixed limits: only to recipients you have allowed, and within a daily and monthly budget (fees included).
• Tamper-proof: every proposal is signed; the wallet checks source, recipient, budget and validity and accepts each proposal only once.
• Full overview: the wallet shows how much of the daily and monthly budget has been used.

How it works

1. Set up a source: scan its QR code in the wallet under “Send” or open its link, and compare the fingerprint.
2. Set allowed recipients (Lightning addresses, domains, bitcoin addresses) and a daily and monthly budget.
3. Open a proposal: the wallet checks it and shows recipient, amount, fee and remaining budget – it pays only once you confirm.

Our approach

Control instead of autopilot: an agent never gets access to your keys and can only propose. The wallet deliberately does not accept Lightning invoices in proposals, because it cannot check their recipient. This way you use the benefits of AI without giving up control over your money.

Good to know: This feature is in beta. The purpose of a proposal is stated by the source; the wallet does not check it.

Open the wallet