User_id is Invalid Field when forwarding a ticket through REST API?

[DrLeisure (Alex Levy)]

I am attempting to create a method to forward a Freshdesk ticket to a specified email address along with an added message. The method and API call work fine, until I add the user_id property to the body of the API call, and then it fails with a 400 status and the message “Unexpected/invalid field in request” This is unexpected because the Freshdesk API Documentation lists user_id as a valid field. What am I doing wrong?

The following data has been anonymized, but the anonymized portions are definitely correct.

Here is the response I am getting:

{
  "description": "Validation failed",
  "errors": [
    {
      "field": "user_id",
      "message": "Unexpected/invalid field in request",
      "code": "invalid_field"
    }
  ]
}

Here is the URI I am using:

POST https://{mydomain}.freshdesk.com/api/v2/tickets/118730/forward

My Headers:

Accept: */*
User-Agent: Thunder Client (https://www.thunderclient.com)
Content-Type: application/json
Authorization: Basic {verified key}=:X

And the body of the request:

{
  "body": "<p>The workflows for this ticket have been completed: '{workflowNumber}'</p><br><br>",
  "user_id": "2043094848729",
  "to_emails": ["{me}@{mycompany}.com"]
}

I should also note that this works perfectly when I remove the user_id from the body of the request, but it fails when user_id is included, regardless of whether it is in string or int format.