Sending AJAX/PHP Variables

I've searched the web for an answer to this several times over but can't seem to find a working solution.

I've excluded a lot of the code for readability & sake of minimalism. The project I'm working on is supposed to open a modal window & load in content from the database.

My problem is that the variable isn't being set in PHP. Literally everything else is working with the exception of this variable pulling through. My code pulls the div id name and matches it in the php file. If they match, the information is pulled from the database. As of right now, my variable is empty... so no match. If I hardcode the variable, it works perfectly - but that isn't helpful in this situation.

I've tried GET, POST, I've tried assigning the value to a cookie. Literally nothing works.

Any ideas would be greatly appreciated.

<div id="despair" class="cartoon" onclick="openEp(this.id)">
<p>content here</p>
</div>

<div id="friday" class="cartoon" onclick="openEp(this.id)">
<p>different content here</p>
</div>

function openEp(clikId) {
episode_name = clikId;

$.ajax({
     type: 'POST',
     url: 'cartoons.php',
     data: ({episode_name: episode_name}),
     success: function(data) {
      console.log('sent ' + episode_name);
     }
    });
}

and for my cartoons.php file

<?php include 'connect.php';

$conn = mysqli_connect(DB_HOST, DB_USERNAME, DB_PASSWORD, DB_DATABASE);

$episode_name = $_POST["episode_name"];

if (isset($_POST["episode_name"]) && !empty($_POST["episode_name"])) {
echo $_POST['episode_name'];
} else {
 echo "not assigned";
}


?>