curl --request POST \
  --url https://vantage-us.abbyy.com/api/publicapi/v1/transactions/{transactionId}/documents/{documentId}/sourceFiles \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: multipart/form-data' \
  --form 'Model={
  "files": [
    {
      "index": 123,
      "registrationParameters": [
        {
          "key": "<string>",
          "value": "<string>"
        }
      ]
    }
  ]
}' \
  --form 'Files=<string>' \
  --form Files.items='@example-file'

{
  "type": "<string>",
  "title": "<string>",
  "status": 123,
  "detail": "<string>",
  "instance": "<string>"
}