AWS API Gateway: Cannot generate mapping template because model schema is missing a 'type' or '$ref' property

I am getting the error:

Cannot generate mapping template because model schema is missing a 'type' or '$ref' property` when trying to define an integration response

I have "type" defined.

My model schema is:

{
  "$schema": "http://ift.tt/1n3c9zE",
  "type": "object",
  "title": "Configuration",
  "properties": {
    "steps": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "ordinal": {
            "type": "integer"
          },
          "rules": {
            "type": "array",
            "items": {
              "properties": {
                "ordinal": {
                  "type": "integer"
                },
                "rId": {
                  "type": "integer"
                },
                "rMId": {
                  "type": "integer"
                },
                "rValue": {
                  "type": "string"
                }
              }
            }
          }
        }
      }
    }
  }
}