> ## Documentation Index > Fetch the complete documentation index at: https://docs.flexprice.io/llms.txt > Use this file to discover all available pages before exploring further. # Implementation Guide > Step-by-step guide to integrating Flexprice Checkout: backend setup, customer redirect, webhook handling, and go-live checklist. This guide covers the complete integration: backend session creation, frontend redirect, webhook handling, and going live. By the end, customers will be able to select a plan, pay, and get an active subscription without any manual step on your side. ## Prerequisites * [ ] Payment provider connected to Flexprice: see [Razorpay Setup](/docs/checkout/razorpay-checkout) * [ ] Required webhook events enabled on your provider dashboard * [ ] Flexprice webhook endpoint registered to receive `checkout.session.*` events * [ ] Customer record exists in Flexprice before the checkout starts * [ ] Plan has at least one non-zero charge ## Architecture ``` Your frontend Your backend Flexprice Razorpay ───────────── ──────────── ───────── ──────── User clicks POST /checkout/ Draft sub + Payment "Subscribe" ───────► sessions ──────► invoice ──► link created Returns URL ◄───────────────────────────────────── Redirect ◄─────────── User pays ──────────────────────────────────────────────────► Checkout ◄── payment_link.paid ────── Activates subscription Finalizes invoice ◄── checkout.session.completed ────────── Fulfill order ◄────── ``` ## Step 1: Create a customer A customer must exist in Flexprice before a session can be created. Create one at sign-up: ```bash theme={null} curl -X POST https://api.flexprice.io/v1/customers \ -H "Authorization: Bearer " \ -H "X-Environment-ID: " \ -H "Content-Type: application/json" \ -d '{ "external_id": "user_12345", "name": "Jane Smith", "email": "jane@example.com", "currency": "INR" }' ``` Use the `external_id` as your reference in subsequent calls. ## Step 2: Create a Checkout Session Call this from your backend only: never expose your API key to the frontend. ```bash theme={null} curl -X POST https://api.flexprice.io/v1/checkout/sessions \ -H "Authorization: Bearer " \ -H "X-Environment-ID: " \ -H "Content-Type: application/json" \ -d '{ "customer_external_id": "user_12345", "action": "create_subscription", "payment_provider": "razorpay", "configuration": { "create_subscription_params": { "plan_id": "plan_pro_monthly", "currency": "INR", "billing_period": "monthly" } }, "success_url": "https://app.example.com/welcome?session_id={CHECKOUT_SESSION_ID}", "failure_url": "https://app.example.com/pricing?error=payment_failed", "cancel_url": "https://app.example.com/pricing", "idempotency_key": "order_" }' ``` Two things worth noting here: * `{CHECKOUT_SESSION_ID}` in `success_url` is a placeholder that Razorpay replaces on redirect. Use it to identify which session the customer just completed. * `idempotency_key` tied to your internal order ID means a retry on timeout gives you back the same session, not a duplicate. Store the returned `id` (`chk_...`) in your database alongside the order. ## Step 3: Redirect the customer Return the `payment_action.url` from your backend to your frontend and redirect immediately: ```javascript theme={null} window.location.href = session.payment_action.url; ``` Do a full-page redirect, not an iframe. The payment link expires after 15 minutes, so don't add unnecessary steps before the redirect. ## Step 4: Handle the webhook Do not rely on the redirect URL to confirm payment: it can be bypassed. The `checkout.session.completed` webhook is the authoritative signal. Register your endpoint in **Settings → Webhooks**, then handle the events: ```javascript theme={null} app.post('/webhooks/flexprice', express.raw({ type: 'application/json' }), async (req, res) => { const { event_type, data } = JSON.parse(req.body); res.status(200).send('ok'); // respond fast, process async if (event_type === 'checkout.session.completed') { // subscription is active, invoice is finalized await grantAccess(data.customer_id); await sendWelcomeEmail(data.customer_id); } if (event_type === 'checkout.session.failed') { await notifyPaymentFailed(data.id); } if (event_type === 'checkout.session.expired') { await clearPendingState(data.id); } }); ``` Make this handler idempotent: Flexprice delivers events at least once. Check whether you've already fulfilled the order before acting. ## Step 5: Handle success and failure pages Use the redirect URLs for UX only, not for fulfillment logic. **Success page**: poll the session to confirm before showing a result: ```bash theme={null} curl https://api.flexprice.io/v1/checkout/sessions/ \ -H "Authorization: Bearer " \ -H "X-Environment-ID: " ``` If `checkout_status` is `completed`, show the success state. If it's still `pending`, the webhook hasn't arrived yet: show a "processing" state and poll again in a few seconds. **Failure or cancel page:** The customer can start over. Create a new session. The previous session and everything it created are cleaned up automatically. ## Step 6: Test the integration Use your provider's test credentials before switching to live keys. For Razorpay test cards and UPI IDs, see [Razorpay Checkout Setup](/docs/checkout/razorpay-checkout#step-4-test-the-flow). After a test payment, verify: * [ ] Session `checkout_status` is `completed` * [ ] Subscription is `active` * [ ] Invoice is `finalized` * [ ] Your backend received `checkout.session.completed` * [ ] Fulfillment ran (access granted, emails sent, DB updated) ## Error reference | Scenario | Response | Fix | | ---------------------------------------------- | ---------------------------------- | ----------------------------------------------------------- | | Customer doesn't exist | 404 | Create the customer before starting checkout | | Plan produces zero-amount invoice | 400 | Use a plan with at least one non-zero charge | | Duplicate `idempotency_key` for active session | 409 | Fetch the existing session; use a new key for a new attempt | | Customer doesn't pay in time | Session expires; drafts cleaned up | Let the user start a new checkout | | `payment_link.paid` not enabled | Subscription stays inactive | Enable the event in your payment provider dashboard | ## Go-live checklist * [ ] Switch provider connection from test keys to live keys * [ ] Confirm all required webhook events are enabled on the production URL (not test) * [ ] `success_url`, `failure_url`, `cancel_url` point to production domains * [ ] Webhook endpoint responds within 5 seconds and uses HTTPS * [ ] Fulfillment handler is idempotent Test credentials and webhook event configuration. Full field reference for the create session call.