Errors

Code	Meaning	What to do
401	Authentication failed: missing headers, unknown or disabled client, bad signature, or timestamp outside ±300 s	Fix signing; check your server clock
401 tenant suspended	Your account is stopped; the credential itself is fine	Contact us
403	Authenticated, but your client lacks the endpoint’s scope	Ask us to add the scope
404	ZIP, license or UPC not found	Treat as no result
422	Invalid or empty request	Fix the request
429	Live verification budget exhausted (verify only); detail names the tier	Back off; use your cached answer
502	ATF upstream failure (verify only)	Use your cached answer; retry later

Every response carries an X-Request-ID header — include it when you contact us about a failed call.

Build for degradation

Treat the API as an enhancement, not a hard dependency: time out after a few seconds, fall back to your last cached answer, and never block a checkout or sale on a lookup.