Using Ajax to call PHP that updates data in MySQL - php

Question

I've been researching this for awhile and there are a lot of similar questions that have been asked. I tried researching as much as I could and came up with a code that should work in theory... but for whatever reason, it just doesn't. I can't seem to figure it out!
I am using JQuery/AJax to call a php file and update SQL records. Here is the general gist of the code. Whats left out is essentially a button click action which calls the ajax function. The Php is going to (eventually) add the StoreID value to an array, serialize it and add it into mysql.
Each piece of the code works on their own, but when put together it just doesn't work!
Java Script Code:
jQuery.ajax({
type: 'POST',
url: 'storeid.php',
data: {StoreID: IDjs[x] },
success: function(reponse) {
$('#error').html('Success! SkipID: ' + IDjs[x]);
onStateNext(); },
error : function(code, message){
$('#error').html('Error Code: ' + JSON.stringify(code) + ', Error Message: ' + JSON.stringify(message));}
});
The weird thing about this code, is that the "Success" functions get output. The success callback is displayed and the proceeding script is run.. despite the fact that it doesn't appear to actually send the StoreID variable to the php file.
The PHP Code (storeid.php):
$test=$_POST['StoreID'];
if (isset($test))
{
global $conn2;
$memberid = $_SESSION['memberID'];
$testarray = array(7,8,$test);
$serialized_data = serialize($testarray);
$insertsql = "UPDATE StoreIDs SET IDs = '$serialized_data' WHERE MemberID = $memberid";
if (mysqli_query($conn2, $insertsql))
{
echo "Updated with StoreID: " . $test;
} else {
echo "Error updating record: " . mysqli_error($conn2);
}
} else {echo "no isset value"; }
This code also works when run without the ajax. It'll properly update the record when called directly by php but not when called by the ajax script above.
Any ideas of what I could have done wrong?

Answer 1

Figured out thanks to #JayBlanchard. You can use the firefox developer tools to see server responses, which allowed to see the error messages and realize that it was communicating but simply not getting the credentials from the database.
Turns out you can't use global variables if the database file isn't included. I thought it didn't need it, since it works fine when running server side, but since ajax is run client side after the server has closed the connections for the database, it needs to be opened again!