FastStar developer documentation

Everything you need to integrate FastStar: the hosted checkout via Checkout Sessions, the browser and Flutter SDKs, saved cards with off-session charges, and signed webhooks — all under your own brand.

Quickstart: five steps to your first payment

1. Create a merchant account

   Sign up for a FastStar merchant account and complete onboarding. In Merchant of Record (MoR) mode you verify your identity online; in Direct/PSP mode your business is reviewed by the platform.

2. Create an API key

   In the merchant dashboard, create an API key. Send it as the X-API-Key header on every server-side request. Never embed the key in a browser or mobile app.

3. Create a Checkout Session on your server

   Your server calls POST /public/checkout/sessions with the products to sell and gets back a hosted checkout url.

   curl https://api.faststarpay.com/api/v1/public/checkout/sessions \
     -H "X-API-Key: YOUR_API_KEY" \
     -H "Content-Type: application/json" \
     -d '{
       "mode": "payment",
       "presentation": "iframe",
       "line_items": [{ "price_id": "price_xxx", "quantity": 1 }],
       "success_url": "https://yoursite.com/success",
       "cancel_url": "https://yoursite.com/cancel"
     }'

4. Open the checkout in your front end

   Include FastStar.js and open the session URL in an overlay (presentation: "iframe"), or redirect the whole page (presentation: "link").

   <script src="https://cashier.faststarpay.com/sdk/v1/faststar.min.js" defer></script>
   <script>
     // data.url comes from your server (step 3)
     FastStar.checkout.open({ url: data.url });   // overlay
     // or: window.location.href = data.url;      // full-page redirect
   </script>

5. Reconcile with webhooks

   Configure a webhook endpoint in the merchant dashboard and fulfill orders on payment.succeeded. Front-end events such as checkout.success are for UI only — always treat the server-side webhook as the source of truth.

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