There was an error during the transport or processing of this request. Error code = 10, Path = /wardeninit
Your client side code never calls getConversations, that is why you don't see it on the console. Among many ways to do this, you could add an IIFE to call that function by adding the following on between <script> tags
(function (){getConversations()}());
By the other hand, the referred error message on the Chrome Developers Tools Console occurs even with the simplest code like the following
function myFunction(){
var html = HtmlService.createHtmlOutputFromFile('index');
SpreadsheetApp.getUi().showModalDialog(html, 'Test')
}
<!DOCTYPE html>
<html>
<head>
<base target="_top">
</head>
<body>
Hello world!
</body>
</html>
So it's not you, it's Google