All errors return RFC 9457 Problem Details with content type application/problem+json.
Error types
Common mistakes
Dates must be YYYY-MM-DD. The API rejects MM/DD/YYYY, 2023-1-5, and ISO timestamps in query parameters.
Unknown series
Series IDs are uppercase: GDPC1, not gdpc1. Use GET /v1/series?q=GDP to search.
Missing API key
See Authentication. The header name is X-API-Key, not Authorization.
Rate limit exceeded
Read the Retry-After header for seconds until reset. See Rate limits for retry strategy. Last modified on March 29, 2026