Flint is a payments API built around the sale. One HTTP API at https://api.withflintpay.com takes card, Apple Pay, Google Pay, Affirm, and ACH debit payments on a Flint-hosted checkout page or inside your own UI. The same API sends invoices, bills subscriptions, and handles the refunds, returns, and disputes that follow. If you want a working payment before reading further, Accept your first payment gets you there with one curl request and a browser.
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Any future expiry, any CVC. Works on every test-mode checkout. See Testing for declines and 3D Secure.
Every payment in Flint settles against an order. The order holds the line items, discounts, fees, tip, and tax, plus two sets of amounts: what is owed and what has been collected or refunded. Flint computes the totals from what you add to the order.
Money reaches the order through one of the surfaces below. They differ in who starts the payment and when it is due. The order is the same whichever one you pick.
| Object | What it is | Guide |
|---|---|---|
| Order | The sale: line items, totals, and payment state | Why Flint is orders-first |
| Product | What you sell. Line items name one of its variants, or a bundle, and get their price from the catalog | Catalog setup |
| Checkout session | A Flint-hosted payment page for one order and one buyer | Checkout sessions |
| Payment intent | One attempt to collect money, in your own UI with Stripe Elements | Embedded Payments |
| Payment link | A reusable URL that creates a new order for each buyer who pays | Payment links |
| Invoice | A bill against an order, with a due date, reminders, and a PDF | Invoicing |
| Subscription | A plan and a saved payment method that create an order every billing cycle | Subscription billing |
| Refund | Money returned against an order | Refunds |
| Customer | A buyer with saved payment methods and a hosted account for orders, returns, and subscriptions | Customer accounts |
Whichever surface collected the money, the order is what you read afterward. Its payment_status and settlement_amounts say what has been paid, refunded, and is still outstanding. Refunds, webhooks, reports, and support all key on order_id.
Payment links, checkout sessions, and invoices are the three hosted ways to collect. A payment link shares one URL among many buyers, a checkout session collects from one buyer right now, and an invoice bills a balance that is due later. Payment links vs checkout sessions vs invoices walks through the choice.
If you are coming from Stripe or Square, the shift is that those APIs start from the charge and Flint starts from the order. Migrating from Stripe and Migrating from Square map the objects field by field.
https://api.withflintpay.com with your key in the Authorization: Bearer header. Every Flint key is secret and belongs on your server. See Authentication.flint_test_... key runs against a sandbox with its own test data. A flint_live_... key charges real money. Same hostname, same request shapes. In test mode, card 4242 4242 4242 4242 with any future expiry and any CVC completes a checkout.{"amount": 2500, "currency": "USD"} is $25.00. See Money & currency.ord_, cs_, pi_, inv_, and ref_ tell you what an id refers to at a glance.Content-Type: application/json. A body over 1,048,576 bytes fails with 413 and the REQUEST_BODY_TOO_LARGE code, so split a larger write into several requests, such as adding an order's line items in batches.data, with a request_id and a meta object. Lists add a next_page_token for pagination. A failure returns an error with type, code, message, and a request_id. See Error handling.Idempotency-Key header. Retry with the same key and you get the original result instead of a duplicate. See Idempotency.POST to your URL and retries until your server confirms receipt. Fulfill from the order.paid event, not from the browser redirect. See Webhooks.One request shows most of these at once:
curl -X POST https://api.withflintpay.com/v1/orders \
-H "Content-Type: application/json" \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Idempotency-Key: order-mug-001" \
-d '{
"line_items": [{
"name": "Ceramic mug",
"quantity": 1,
"inventory_requirement": "not_tracked",
"unit_price_money": {"amount": 2500, "currency": "USD"}
}]
}'
{
"data": {
"order_id": "ord_1kmn0aExample",
"status": "open",
"payment_status": "unpaid",
"pricing_amounts": {
"total_money": {"amount": 2500, "currency": "USD"}
},
"settlement_amounts": {
"outstanding_money": {"amount": 2500, "currency": "USD"}
},
"line_items": [...]
},
"request_id": "0b8f2b26-9c1e-4f6a-8d35-7e4a2c9b1d60",
"meta": {"api_version": "2026-02-01"}
}
@flintpay/node and flintpay/flint give TypeScript, JavaScript, and PHP integrations typed request and response shapes over every public operation.flint API command maps to a /v1 route, and flint listen forwards your sandbox's webhook events to localhost without a public tunnel./SKILL.md, and the OpenAPI spec at /v1/openapi.json.SANDBOX_SELECTION_REQUIRED means.order.paid and the other events your integration acts on.Was this helpful?