SERP API Error Codes and Recovery Strategy

400 means request design problem

A 400 response usually means required input is missing or malformed. For SERP workflows, common causes include missing q values, invalid parameter combinations, or application code that drops part of the request during serialization.

401 means auth path problem

A 401 should send you into header and service-key debugging, not retry logic. Confirm x-api-key usage, verify the secret came from the correct environment, and check that the service key matches the SERP endpoint family.

402 means plan or quota state problem

A 402 is usually not something code can fix by itself. Move into operator messaging, usage checks, or plan review. User-facing products may need cached fallbacks or delayed-processing states instead of repeated failures.

429 means controlled retry required

Treat 429 as temporary throttle pressure. Use exponential backoff, queue-based retries, and concurrency control rather than immediate loops. Log enough request context to see which workloads are creating the burst.

switch (statusCode)
{
    case 429:
        await Task.Delay(TimeSpan.FromSeconds(Math.Min(60, Math.Pow(2, attempt))), cancellationToken);
        break;
}

504 often means workflow should move to async

A sync timeout does not always mean the data request failed permanently. It often means the job should continue through an async polling path or through a calmer queued retry pattern. Teams using larger batch jobs should design for that transition early.

Store error context with the request context

Production debugging gets easier when every error record also keeps query, locale, device, timestamp, execution mode, and request source. That makes it possible to distinguish bad inputs from market-specific or load-specific problems.

Map each error to one next action

The biggest reliability upgrade is often procedural: 400 fix request, 401 fix auth, 402 alert usage owner, 429 retry calmly, 504 continue via async or fallback. When each code maps to one primary action, on-call response becomes much faster.