curl --location --request POST '/esign/documents//send/' \
--header 'Authorization: <api-key>'{
"message": "string",
"document_id": "b792e8ae-2cb4-4209-85b9-32be4c2fcdd6",
"signing_url": "http://example.com",
"status": "draft",
"sent_at": "2019-08-24T14:15:22.123Z"
}