PHP cannot read incoming post data

Hi,

I've created my own custom application in PHP and 2 hours ago sent it to my OVH hosting catalog. Ever since then it's been nothing but problems.

My frontend sends to the backend data from a form in the following way with jQuery:

let formData = $('#token-form').serialize();
var requestForTokens = $.ajax('file.php', {
method: 'post',
data: formData,
contentType: "application/json",
dataType: "json",
encoding: "text/plain"
});

(there's only one input named "access-token")

On the backend I have the following code to verify incoming data:

if ($_SERVER["REQUEST_METHOD"] == "POST") {
$postData = json_decode(file_get_contents('php://input'), true);
$token = $postData['access-token'] ?: null;
if (empty($token)) {
http_response_code(401);
$response['error_message']='Token cannot be empty';
//much more code later

Of course every request ends up with the empty token message.

Before I didn't have the 'contentType: "application/json"' in my ajax request and I was just using "$_POST['access-token']" to get contents of the incoming data, but the the server always responded with 400.

Please help. On my xampp localhost it worked perfectly, no problem. With OVH I constantly stumble upon every possible error.