What is the JSON syntax for a referencing on object type using an external import?

[Jacob Olson]

I am testing external imports and have run into a problem with referencing object types. I have tested the JSON for external imports without referencing object types, and had no problem. For that I used the JSON structure that Atlassian Developer provided: https://developer.atlassian.com/cloud/insight/imports/schema-and-mapping/#reference-type-attributes

Atlassian Developer also provides a JSON guide that includes referencing object types: https://api.atlassian.com/jsm/insight/imports/external/schema/versions/2021_09_15

I have been trying to follow their JSON for referencing object types but I keep getting this error: 

{

    "jsonValidationErrors": [

        {

            "type": "required",

            "code": "1028",

            "path": "$.schema.objectSchema.objectTypes[1].attributes[12]",

            "arguments": [

                "referenceObjectTypeName"

            ],

            "details": null,

            "message": "$.schema.objectSchema.objectTypes[1].attributes[12].referenceObjectTypeName: is missing but it is required"

        }

    ],

    "dataValidationErrors": [],

    "status": "error"

}

I am wondering if anyone can help me to understand what the error is referencing, and what I can do to fix it?

Thank you!

[Jacob Olson]

I was reviewing the information at the Atlassian Developer website and found something I was missing. For the attributes that are referencing other attributes I used this format:
{
"name":"UserID",
"description":"",
"type":"referenced_object",
"referenceObjectTypeName":"users"
}

In the Mapping, I used this format:
{
"attributeName": "UserID",
"attributeLocators": [
"UserID"
],
"objectMappingIQL": "UserID is not EMPTY"
}

I was not including the object mapping IQL, and I was not correctly specifying the "type" and "referenceObjectTypeName" in the object type.