401 means the API key is missing, malformed, or revoked. Check Settings → API keys to confirm the key is still active.
402 means the call would have spent more credits than the account has. Top up at /pricing or set auto-refill.
413 means the uploaded file exceeded the per-tool size limit (100 MB for PDF tools, 20 MB per image for Image to PDF). 422 means the PDF parsed successfully but is corrupt or password-protected; unlock it first.