What happened
The attachment exists, but its file bytes have not been uploaded.
How to fix it
PUT the file to the upload_url from POST /v1/attachments, then retry the read or send.
This error is safe to retry. Wait for the Retry-After header when it is present. If the endpoint takes an Idempotency-Key, reuse the same key so a retry never creates a duplicate.
Example response
An illustrative example. The message wording and the contents of details vary; branch on error.code.
Still stuck?
Email support@blujay.io with the trace_id from the error response. See Errors for the response format. 
