Proxy error: UnprocessableEntity - When make a request to external API

Hi,

I'm testing our application locally using zat server and I've receiving this message Proxy error: {:code=>"UnprocessableEntity", :status=>"422", :title=>"Unprocessable Entity", :message=>"Failed to get installation and oauth information for app."} when a request is made locally to our server API. 

below is the code to generate the header for the API request

request(params) {
  const settings = Object.assign({
    type: 'GET',
    secure: true,
    contentType: 'application/json',
    headers: {
      Authorization: 'Basic {{setting.ApiToken}}',
      Accept: `application/vnd.${API_VERSION}`,
    },
  }, params);

  return this.client.request(settings);
}

 note: ZenDesk App works in production