HTTP status codes: Why your API integrations fail and how to fix them

API integrations fail predictably. A 429 from Stripe during peak transaction volumes. A 503 from your payment gateway at month-end. A 502 from AWS API Gateway because Lambda timed out. The question isn't whether you'll hit these errors, it's whether your retry logic handles them correctly.

The pattern is consistent across enterprise integrations: 4xx errors are your problem, 5xx errors are theirs. Worth noting: this breaks down at the edges. A 429 rate limit is technically your fault, but it requires server-side cooperation (Retry-After headers) to solve properly. A 403 could be your misconfigured permissions or their broken RBAC. Context matters.

What actually works

Three strategies separate robust integrations from brittle ones:

Exponential backoff for 5xx errors. When Stripe returns a 503, your first retry at 1 second won't help. The service is down. Try again at 2s, 4s, 8s. AWS recommends this for API Gateway timeouts. Spring Boot's @Retryable annotation implements it, but watch your max attempts. Five retries at exponential intervals can mean 31 seconds of hung requests.

Rate limit respect for 429. Read the Retry-After header. If Stripe says wait 60 seconds, wait 60 seconds. Shopify's REST Admin API enforces this strictly. Ignoring it gets your integration throttled harder. The math changes if you're batching: better to queue requests than hammer the endpoint.

Idempotency keys for payment retries. The 502/503 distinction matters less than ensuring you don't charge twice. Stripe's idempotency keys (valid for 24 hours) let you safely retry failed payments. This isn't optional for financial transactions.

The real cost

API providers keep improving error documentation because vague 400 responses cost engineering teams hours per integration. The HTTP standards define ~60 codes, but implementation inconsistency causes more problems than missing codes. When your gateway returns a generic 500 instead of a specific 504 timeout, you can't tune retry logic properly.

History suggests the gap between standards and practice won't close soon. AWS API Gateway has a hard 30-second timeout limit. You can't increase it. You architect around it or you switch to async patterns. That's the constraint that matters, not whether you remember that 418 means "I'm a teapot."

The pattern holds: specific errors enable specific solutions. Generic errors waste time.