Your value for `channelUrl` is nominally correct. If I set up my XAMPP server, via `httpd.conf` to use port 8000, then this HTML page works perfectly fine for me: <!DOCTYPE html> <html><head> <title>StackApps SDK auth test</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head><body> <p>See the console.</p> <script type='text/javascript' src='https://api.stackexchange.com/js/2.0/all.js'></script> <script type="text/javascript"> SE.init ( { clientId: 1543, key: '{USE YOUR OWN KEY}', channelUrl: 'http://localhost:8000/test/blank.htm', complete: function (data) { console.log ("Init: ", data); } } ); </script> </body></html> -- where `blank.htm` is a completely empty file and I access the page with this URL: `http://localhost:8000/test/StckApps%20SDK%20auth%20test.htm` The console shows: Init: Object { version="11633"} So, something you are not showing us is the problem. (Redirects? Using `file://` protocol? Typos? Other?) ---------- However, there is an apparent bug in the SDK. It apparently **does not account for ports when you try to do the next step (`SE.authenticate()`).** Consider this page: <!DOCTYPE html> <html><head> <title>StackApps SDK auth test</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> </head><body> <p>See the console.</p> <p><button id="authBtn">Get authorized.</button></p> <script type='text/javascript' src='https://api.stackexchange.com/js/2.0/all.js'></script> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script> <script type="text/javascript"> $(document).ready (jQueryMain); function jQueryMain () { $("#authBtn").click ( function () { SE.authenticate ( { success: function (data) { console.log ("Auth success: ", data); }, error: function (data) { console.log ("Auth error: ", data); }, scope: ['read_inbox'], networkUsers: true } ); } ); } </script> <script type="text/javascript"> SE.init ( { clientId: 1543, key: '{USE YOUR OWN KEY}', channelUrl: 'http://localhost:8000/test/blank.htm', complete: function (data) { console.log ("Init: ", data); } } ); </script> </body></html> When I click on the <kbd>Get authorized.</kbd> button, a popup appears with a valid access token in the URL. But this information never gets back to the calling page! The Firefox Error Console reports: > Security Error: Content at `http://localhost/` may not load data from `http://localhost:8000/test/StckApps%20SDK%20auth%20test.htm`. Note the port mismatch in what the SDK tries to use? **This looks like a bug.** If I change the page, edit my [app settings][1], and reset XAMPP to use `localhost` without any port specified (except 80 in httpd.conf), then the page works perfectly and I get a response like: > Auth success: Object { accessToken="72L6...2W6cH(kQ))", expirationDate=Date, networkUsers=[23]} in the Firebug console. ---------- So, even if you get the first part working, you do not want to use a non-default port with the SDK, anyway, until the SDK bug is fixed. [1]: http://stackapps.com/apps/oauth/