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Pay As You Go (PAYG) — Developer Guide

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Pay As You Go (PAYG) — Developer Guide

PAYG lets developers purchase API access through Stripe Checkout and convert that completed payment into a short-lived API session.

Quick Start

1. Check current pricing

Terminal window
curl https://api.bloqr.dev/api/payg/pricing

2. Create a Checkout Session

Terminal window
curl -X POST https://api.bloqr.dev/api/stripe/payg/checkout \
  -H 'Content-Type: application/json' \
  -d '{ "requestsToPurchase": 10 }'

Response:

{
  "success": true,
  "checkoutUrl": "https://checkout.stripe.com/...",
  "sessionId": "cs_test_..."
}

3. Exchange the completed payment for a PAYG session

After Checkout redirects back to the app, send the completed Checkout Session ID or PaymentIntent ID to the authenticated session-creation endpoint:

Terminal window
curl -X POST https://api.bloqr.dev/api/payg/session/create \
  -H 'Content-Type: application/json' \
  -H 'Cookie: better-auth.session_token=<your-session-token>' \
  -d '{ "checkoutSessionId": "cs_test_..." }'

Response:

{
  "success": true,
  "sessionToken": "payg_...",
  "requestsGranted": 10,
  "expiresAt": "2026-05-27T23:00:00.000Z"
}

4. Use the PAYG session

Terminal window
curl https://api.bloqr.dev/api/compile \
  -H 'X-Payg-Session: payg_...' \
  -H 'Content-Type: application/json' \
  -d '{ ... }'

The response includes X-Payg-Session-Remaining.

5. Check authenticated usage totals

Terminal window
curl https://api.bloqr.dev/api/payg/usage \
  -H 'Cookie: better-auth.session_token=<your-session-token>'

x402 Protocol

Endpoints protected by paygMiddleware() follow the x402 protocol:

  1. Without a session: the API returns 402 Payment Required with a JSON body plus X-Payment-Required.
  2. With X-Payment-Response: the middleware verifies the Stripe payment proof, issues or reuses the deterministic PAYG session, consumes one request, and continues the request.
  3. With X-Payg-Session: the middleware validates the session, decrements usage, and returns X-Payg-Session-Remaining.

Payment specification shape

{
  "version": "2",
  "scheme": "exact",
  "network": "stripe",
  "maxAmountRequired": "1",
  "resource": "price_...",
  "description": "Pay As You Go - $0.01 per API call",
  "mimeType": "application/json",
  "outputSchema": null,
  "extra": {
    "stripePublishableKey": "pk_live_...",
    "checkoutUrl": "https://api.bloqr.dev/api/stripe/payg/checkout",
    "sessionRequestsGranted": 10,
    "sessionTtlSeconds": 3600
  }
}

Session Lifecycle

PAYG sessions are intentionally deterministic per PaymentIntent:

  • A successful Stripe payment creates or reuses exactly one PaygSession.
  • Replaying the same paymentIntentId or checkoutSessionId returns the same session token instead of minting unbounded access.
  • Sessions expire after one hour unless exhausted earlier.
flowchart TD
  Payment["Stripe payment succeeds"] --> Event["payment_intent.succeeded or checkout.session.completed"]
  Event --> PaymentEvent["PaygPaymentEvent upsert"]
  PaymentEvent --> Session["PaygSession create / reuse"]
  Session --> Consume["API request consumes remainingRequests"]
  Consume --> Renew["402 + new Checkout when exhausted or expired"]

Usage Accounting

GET /api/payg/usage returns:

  • totalRequests / totalSpendUsdCents from PaygCustomer
  • thisMonthRequests / thisMonthSpendUsdCents from current-month PaygPaymentEvent rows
  • conversionEligible once cumulative spend crosses PAYG_CONVERSION_THRESHOLD_USD_CENTS

This makes PAYG upsell prompts deterministic and keeps monthly reporting tied to Stripe payment events.

Database Models

PaygCustomer

Stripe customer-level running totals for PAYG usage.

PaygPaymentEvent

Append-only reconciliation log keyed by stripePaymentIntentId.

PaygSession

Opaque API session token used by X-Payg-Session.

BillingUsageEvent

General usage ledger for rolling 30-day billing and future Stripe metering exports.