ZAFClient requests returning 500 starting today

Hello,

We use `ZAFClient.request()` to make requests to a url on our server that generates our app's UI for our Zendesk app. This has worked fine for many months and nothing has changed our side but now making the request is generating a 500 and our app UI has stopped rendering (shows up blank in the Zendesk sidebar).

Here's the gist of the code that makes the request...

```

  console.log("getInitialFeedbackForm running...");
  var url = "https://url_to_our_server/app/integrations/zendesk/app/form/";

  var settings = {
    url: url,
    headers: {'ZENDESKAPPTOKEN': '{{setting.token}}'},
    cache: false,
    secure: true,
    cors: false,
    type: 'GET'
  };
  console.log("settings");
  console.log(settings);
  client.request(settings)
    .then(function(response) {
      replaceForm(response, client, baseUrl);
    })
    .catch(function(response) {
      if(response.status == 401) {
        $("#form-container").html(response.responseText);
      }
      else {
        console.log("Error:");
        console.log(response);
      }
    });
    client.invoke('resize', { width: '320px', height: '610px' });

```

I can see our js is run but the call to ` client.request(settings)` is throwing a 500.

```

{readyState: 4, responseText: 'Internal server error', status: 500, statusText: 'error'}

```

We can see that the url requested via `ZAFClient.request()` never hits our server which makes me think something is going wrong on Zendesk's end.

How can we find out why the call to the proxy is failing?