title: Previewing failed, but deployment works
body: <p><strong>Background:</strong></p>
  
  <p>I'm quite new to App Maker, but have been involved in programming/IT for over 2 decades.</p>
  
  <p>I have created an App Maker app, which works fine.  It is deployed, and functions internally in our organization.</p>
  
  <p>It accesses a Team Drive spreadsheet, makes modifications to it based on input criteria, and sends an email out to a hardcoded user.  It uses no external GCP database or other resource.</p>
  
  <p>The OAuth scopes it requires are:</p>
  
  <ul>
  <li>admin.directory.user.readonly</li>
  <li>drive.readonly</li>
  <li>script.send_mail</li>
  <li>spreadsheets</li>
  <li>userinfo.email</li>
  </ul>
  
  <p><strong>Problem:</strong></p>
  
  <p>I can no longer preview the app.</p>
  
  <p>When I click on "Preview" at the top right, a new tab opens and a spinning wheels seems to indicate that the preview is loading.  Within about 4 seconds, the tab closes and the original tab (with the scripts, UI etc) gives a "Previewing failed.  Dismiss" error in the bottom centre.</p>
  
  <p>I am both able to deploy the exact same code/UI/etc, as well as run it without issue.</p>
  
  <p>I do not know what I changed, since being able to preview the app, but cannot seem to regress to that state.</p>
  
  <p><strong>What I've tried:</strong></p>
  
  <p>Admittedly not much, as I don't know where to look.  I'm rather certain that there must be some setting somewhere, but for all my googling, I've come up empty.</p>
  
  <p>This can't be a client/server script or other syntax issue, as otherwise the deployment also wouldn't work.</p>
  
  <p>With a more meaningful error, I would know where to look.</p>
  
  <p><strong>Expected Result:</strong></p>
  
  <p>Obviously, I should be able to preview the app if it is deployable.</p>