POST /customers/v1/transactions/{id}/documents.{
"id": "497f6eca-6276-4993-bfeb-53cbbbba6f08",
"status": "PENDING",
"upload_url": "http://example.com",
"upload_expires_at": "2019-08-24T14:15:22.123Z",
"required_headers": {
"Content-Type": "string",
"Content-Length": "string",
"x-amz-checksum-sha256": "string"
}
}