Wrong response for invalid type value

Currently if I try to create a resource with a wrong type value, the response will be the following:

HTTP/1.1 400 Bad Request
{
  "errors": [
    {
      "title": "Invalid resource",
      "detail": "abc is not a valid resource.",
      "code": "101",
      "status": "400"
    }
  ]
}

But as stated in the jsonapi specifications, it should actually be a 409 Conflict:

A server MUST return 409 Conflict when processing a POST request in which the resource object’s type is not among the type(s) that constitute the collection represented by the endpoint.

Start by tracing the POST resource-creation path that handles an invalid type and locate where the current 400 response is selected. Compare the existing behavior with the JSON:API specification cited in the issue, then verify that this case returns 409 Conflict without changing other invalid-resource responses.