Payment API Monitoring#

Payment processing is the lifeblood of online business. When payment APIs fail, you lose revenue immediately. APIAssert helps you detect payment issues before customers abandon their carts.

The Problem#

Payment API failures are uniquely painful:

• Silent failures — API returns 200 but transaction fails
• Partial outages — Specific card types or methods fail
• Gateway issues — Third-party payment provider has problems
• Validation errors — Your integration rejects valid requests

A 5-minute payment outage during peak hours can cost thousands in lost sales.

How APIAssert Helps#

Monitor Payment Gateway Health#

Check that your payment provider is operational:

Monitor: Stripe Health Check
URL: POST https://api.stripe.com/v1/payment_methods
Assertions:
  ✓ Status code == 200
  ✓ $.object == "payment_method"
  ✓ Response time < 2000ms

Validate Your Payment Integration#

Ensure your own payment endpoints work:

Monitor: Checkout Payment Validation
URL: POST /api/payments/validate
Body: {"amount": 100, "currency": "USD", "method": "card"}
Assertions:
  ✓ $.valid == true
  ✓ $.available_methods contains "card"
  ✓ $.min_amount <= 100

Check Webhook Endpoints#

Verify your webhook handlers are responding:

Monitor: Payment Webhook Health
URL: POST /webhooks/stripe
Assertions:
  ✓ Status code == 200
  ✓ Response time < 500ms

Critical Assertions for Payment APIs#

Transaction Creation#

// Expected response from payment creation:
{
  "id": "txn_abc123",
  "status": "pending",
  "amount": 9999,
  "currency": "usd"
}

Assertions:

• $.id must exist
• $.status must be one of ["pending", "succeeded", "processing"]
• $.amount must equal expected amount
• $.currency must equal expected currency

Payment Status#

// Expected response from status check:
{
  "status": "succeeded",
  "paid": true,
  "receipt_url": "https://..."
}

Assertions:

• $.status must exist
• $.paid must be boolean
• $.receipt_url must match URL pattern

Refund Processing#

// Expected refund response:
{
  "id": "re_xyz789",
  "status": "succeeded",
  "amount": 5000
}

Assertions:

• $.status must equal "succeeded"
• $.amount must be positive integer
• $.id must start with "re_"

Real-World Example#

The Scenario#

A SaaS company processes subscriptions through Stripe. Occasionally, webhook deliveries fail silently, causing subscription renewals to not be recorded — leading to users being incorrectly downgraded.

The APIAssert Solution#

Monitor 1: Stripe Webhook Endpoint

URL: POST /webhooks/stripe
Headers:
  Stripe-Signature: test_signature
Body: {"type": "test"}
Assertions:
  ✓ Status code == 200 or 400
  ✓ Response time < 1000ms

Monitor 2: Subscription Status API

URL: GET /api/subscriptions/health
Assertions:
  ✓ $.queue_size < 100
  ✓ $.last_processed within 5 minutes
  ✓ $.error_rate < 0.01

The Outcome#

• Webhook endpoint availability monitored every minute
• Alert triggered when queue size exceeded threshold
• Team discovered Redis connection issue before customer impact
• Implemented fix and added permanent monitor

Payment Providers to Monitor#

Stripe#

PayPal#

Your Payment Endpoints#

Best Practices#

Use Test/Sandbox Endpoints#

Most payment providers offer test endpoints:

Production: api.stripe.com
Sandbox: api.stripe.com (with test keys)

Monitor both:

• Sandbox — verify your integration works
• Production — catch production-specific issues

Monitor from Multiple Regions#

Payment latency matters globally:

US East:    Monitor latency to Stripe US
Europe:     Monitor latency to Stripe EU
Asia:       Monitor latency to Stripe APAC

Different regions may have different performance characteristics.

Set Aggressive Alert Thresholds#

For payment APIs, detect issues fast:

• Check interval: Every 30-60 seconds
• Alert threshold: 1-2 failures (not 3-5)
• Response time: Alert if > 3 seconds

Create Payment-Specific Alerts#

Route payment alerts to specialized channels:

Payment API Down → PagerDuty (immediate page)
Payment Slow → Slack #payments (warning)
Webhook Queue Growing → Email (monitor)

Test Edge Cases#

Monitor for specific scenarios:

• Zero amount — free trials, $0 checkouts
• Large amounts — high-value transactions
• Currency handling — multi-currency support
• Declined cards — proper error handling

Alert Response Runbook#

When payment alerts fire:

1. Check provider status — Is Stripe/PayPal having issues?
2. Check your logs — Recent deployments? Error spikes?
3. Test manually — Can you process a test payment?
4. Check dependencies — Database, Redis, webhooks working?
5. Escalate if needed — Contact payment provider support

Getting Started#

1. Identify payment flows — Checkout, subscriptions, refunds
2. Map API endpoints — Both yours and provider's
3. Create monitors — Start with transaction creation
4. Add assertions — Validate response structure
5. Set up alerts — PagerDuty for critical, Slack for warnings

Related Use Cases#

• E-commerce API Monitoring — Full e-commerce monitoring
• Webhook Reliability — Monitor webhook endpoints