Ajax Internal Error, jqXHR: underfined - php

Question

Ive butchered my code trying to find this bug. I have a Ajax post function working elsewhere on my code and it works fine.
For some reason this one does not want to cooperate.
Im going to reduce the amount of inputs so the code doesnt look too long.
Here is the php
<?php
// --------Connect to DB --->
include 'connect.php';
$conn = connect ();
//====================================================================>
//grab data
$this_id = $_POST('pid_num');
$this_start_date = $_POST('date_ammend');
$sql_update_query = "UPDATE Galaxy_jobs SET date ='$this_start_date' WHERE PID = $this_id";
//====================================================================>
mysqli_query ($conn,$sql_update_query);
//close
mysqli_close($conn);
?>
Here is my Ajax call.
function ammend_job()
{
pid = '2'; // test figures
start_date_ammended = '11-11-1111'; // test figures
var Data = {
pid_num : pid,
date_ammend : start_date_ammended,
};
$.ajax({
url:"ammend_job.php",
type: "POST",
dataType: 'text',
data: Data,
success: function(data){
if(data.status == 'success')
alert('Post has been uploaded to Database');
},
error: function(xhr,textStatus,err,jqXHR) {
console.log("readyState: " + xhr.readyState);
console.log("responseText: "+ xhr.responseText);
console.log("status: " + xhr.status);
console.log("text status: " + textStatus);
console.log("error: " + err);
console.log("Jquery error:" + jqXHR)
// alert('There is an error, screenshot this error and send to Admin : TextStatus: ' +textStatus+" - Error: "+errorThrown+" - XMLRequest: "+XMLHttpRequest+"- Response Text"+xhr.responseText);
}
});
}
Here are the error codes :
main.php:102 readyState: 4
main.php:103 responseText:
main.php:104 status: 500
main.php:105 text status: error
main.php:106 error: Internal Server Error
main.php:107 Jquery error:undefined
Any help will be greatly appreciated.

Answer 1

It took a while.
I wouldnt have found it if it wasnt for user : tereško who suggested to look closely at the errorlog on the server.
I found that when I replaced my code in php file
//grab data
$this_id = $_POST('pid_num');
$this_start_date = $_POST('date_ammend');
with the square brackets
//grab data
$this_id = $_POST['pid_num'];
$this_start_date = $_POST['date_ammend'];
The code didnt throw an error and worked.
I hope somebody else out there finds this post and figures out that this may be 1 reason for their error.