Site in folder of sub-domain's ajax calls return error 500

Question

I am building website under subdomain. Site path is following: www.sub.example.com/site

In that folder I have functions.php which I use to fire up php functions.

$.ajax({
  type: "POST",
  url: "http://sub.example.com/site/functions.php",
  data: { 
    action: 'sendData',
    data: exampleData
  },
  success: function(data){
    console.log(data);
  }
});

For reasons unknown Chrome's console return:

 POST http://sub.example.com/site/functions.php 500 (Internal Server Error)
 send        @    jquery-3.2.1.min.js:4
 ajax        @    jquery-3.2.1.min.js:4
 (anonymous) @    main.js:35
 dispatch    @    jquery-3.2.1.min.js:3
 q.handle    @    jquery-3.2.1.min.js:3

I have double checked that function file has no errors.

Php file: here

Answer 1

I finally fixed it. Reason was I used wrong sql syntax. I was trying to update row's cert value by inserting new one. What I needed to do is just update the existing one with new value.

What I had:

$addAmount = $conn->prepare("INSERT INTO data (certs) VALUES (:newAmount) WHERE place = :place");

What I needed:

$addAmount = $conn->prepare("UPDATE data SET certs = :newAmount WHERE place = :place");

Thanks everyone for helping.