在LIVE服务器上使用Ajax Post时如何处理503错误消息？

My app works fine on my local machine. I'm able to perform all Ajax calls perfectly. Tested thoroughly on several web browsers and everything works seamlessly on localhost. Problems are now happening on live server. While some Ajax calls work, the most important one which is register.php does not. Upon contacting my host, they told me they can't help me since it's outside their scope which is fine I'm on my own. But is a 503 not something they should handle? They told me the php.ini is read-only(shared hosting)... So does it mean I'm doom or what am I doing wrong here? Php is activated on livesite and I also have a live database(mariadb). I'm using phpmailer in the register.php script but they told me I was allowed to use it. Any help?

This is the error I receive in the console on live site :

Since it is a 503 server-side error I would try re-uploading the problem files since the other files seem to be working. Maybe some files got corrupted during transfer. Let us know if you solve it and what the problem was.