PHP/MYSQL Log-in update troubles - php

Question

I have been working on this Login script for awhile and everything works, except this update function. I have tried changing variable name and everything else. On UpdateUser.php, the code works if I insert variables instead of the $[POST] variables. I am at a loss. Any help would be greatly appreciated. Sorry for the messy code, this is a class assignment, so I wasn't worried about password security at the moment.
This is index4.php
<form id="form" action="index4.php" method="post">
<h2>Update Your Login</h2>
UserName:<br>
<input type="text" id="useuserName" required />
<br>
Password:<br>
<input type="text" id="usepassWord" required />
<br>
First Name:<br>
<input type="text" id="usefirstName" required />
<br>
Last Name:<br>
<input type="text" id="uselastName" required />
<br>
<input id="updateuser" type ="submit" />
</form>
<script>
$('#updateuser').click(function() {
var useID = $_SESSION["id"];
var useuserName = $("#useuserName").val();
var usepassWord = $("#usepassWord").val();
var usefirstName = $("#usefirstName").val();
var uselastName = $("#uselastName").val();
var usePermissions = $_SESSION["Permissions"];
$.ajax({
type : 'POST',
url : '',
data :{action:'updateuser', useID:useID, useuserName:useuserName, uselastName:uselastName, usePermissions:usePermissions},
error: function (html) {
alert( "What the duck" );
},
});
});
</script>
This is the UpdateUser.php file
<?php
//Update
if($_POST['action'] == 'updateuser'){
//Set Variables
$servername = "localhost";
$username = "root";
$password = "";
$db = "userdb";
//Create connection
$conn = new mysqli($servername, $username, $password, $db);
// Check connection
if ($conn->connect_error) {
die("Connection: Failed! " . $conn->connect_error);
}
//Actual Code
$useID = $_POST['useID'];
$useuserName = $_POST['useuserName'];
$usepassWord = $_POST['usePassword'];
$usefirstName = $_POST['usefirstName'];
$uselastName = $_POST['uselastName'];
$usePermissions = $_POST['usePermissions'];
//Create Query
$sql = "UPDATE users SET userName = '$useuserName', Pass = '$usepassWord', firstName = '$usefirstName', lastname = '$uselastName', Permissions = '$usePermissions' WHERE id =" . $useID ."";
//Did it work Check
if ($conn->query($sql) === TRUE) {
echo "Cool";
} else {
echo "What " . $conn->error;
}
//Close Out
$conn->close();
}
?>