POST /manage/v1/user "You haven't filled in some mandatory fields"

Hi, 

I am creating users via the API and it was working up until recently (not sure exactly when it stopped working). 

Now I am getting the following error:

{
  "name": "Bad Request",
  "message": [
    {
      "field": "userid",
      "message": "You haven't filled in some mandatory fields"
    }
  ],
  "code": 1002,
  "status": 400
}

This is the body that is being sent (data scrubbed):

{
	"email": "test@Test.com",
	"password": "password",
	"firstname": "Test",
	"lastname": "User",
	"additional_fields": {
		"8": "Test Field 8",
	  	"9": "Test Field 9",
		"15": "Test Field 15",
		"18": "Test Field 18",
		"22": "Test Field 22"
	}
}

Before the userid, was not required for this end point? I thought that the userid was generated by docebo, upon user creation ? All the Mandatory fields for the additional fields are populated and valid, I have checked that already, just not sure if there was some other change.

Thanks,

Ben