I have build a online live chatroom with lots of work proccessed with ajax. But after i uploaded the files into the infinityfree server. it says
index.php:1 XMLHttpRequest cannot load https://infinityfree.net/errors/403. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://chatman.epizy.com' is therefore not allowed access. The response had HTTP status code 403.
It’s trying to load the page from infinityfree.net/errors/403. Unless you entered that URL yourself, it means that the file or script you were actually trying to send an ajax request to return a 403 Forbidden error response. So this sounds like and issue on your website and not the server.
The first thing I would check is check the Network tab of your browser’s development tools, which will show all the requests your browser makes, including the original ajax request. That should allow you to check whether the ajax request is initiated successfully (correct URL and parameters) and the response returned for that request.