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HTTP 422. The file failed the malware scan and was not stored.

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What it means

Documents (PDF, Office files, archives) are malware-scanned before Flow keeps or sends them. This one was flagged, so it was neither stored nor sent. Images, audio and video are not scanned. If the scan could not run at all, the upload answers a retryable 500 api_error with Retry-After instead, and nothing is stored: retry with the same Idempotency-Key. (A file a person sent that Flow did not keep arrives as a file_blocked message in message.received, which is not this error; its reason says why, scan_failed when Flow could not scan it.)

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Why it happens

  • The file contains malware, or macros the scanner flags.

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How to fix it

Send a different file. If you believe it is clean, export it again from its source (for example print to PDF) and upload that.
Every error also carries hint, one sentence specific to your request, and doc_url, this page. Coding agents connected to Flow’s MCP server (https://api.flow.engineer/mcp) can call explain_error with the type to read this page.