Use this operation to upload the file to be signed for a signature request.
The SHA256 hash of the uploaded file must be equal to the
hashToSign property of the signature request or the upload fails.
Once uploaded, the file is stored and the
fileURL property of the signature request is set, so that it can be used by a signature application to download and present the file to the signers.
Only stateless signature requests or stateful signature request in DRAFT state can be updated.
WARNING: the storage of the file to be signed is provided for convenience only: it is not required, and you should never upload a file if you have any concern about its privacy.