JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
<link rel="stylesheet" href="code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<script src="https://elder-scrolls-online.eu/datenbank/ajmanager/ajaxmanager.js"></script>
<p>
  <label class="item-slider" for="amount">Stufe:</label>
 <input class="item-slider" readonly id="amount">/
  <input class="item-slider" readonly id="amount2" value="50">
</p>
 
<div id="slider-vertical" style="height:10px;"></div>

CSS

.ui-widget.ui-widget-content {
    border: 1px solid #c5c5c5;
    width: 100%;
}

.ui-state-default, .ui-widget-content .ui-state-default, .ui-widget-header {
    border: 1px solid #444 !important;
    background: none !important;
}

.ui-slider .ui-slider-handle {
    position: absolute;
    z-index: 2;
    width: 1.2em;
    height: 1.2em;
    cursor: default;
    -ms-touch-action: none;
    touch-action: none;
}

.ui-widget.ui-widget-content {
    border: 1px solid #c5c5c5;
    background-color: #353232;
}

.ui-slider-horizontal .ui-slider-range-min {
    left: 0;
    background-color: #817373!important;
}

JavaScript

jQuery(function ($) {

	var ajaxManager = $.manageAjax.create('cacheQueue', {
		queue: 'clear',
		cacheResponse: true,
		preventDoubleRequests: true,
		abortOld: true
	});
  
  // Slider Script

	$("#slider-vertical").slider({
		orientation: "horizontal",
		range: "min",
		min: 1,
		max: 50,
		value: 50,
		slide: function (event, ui) {
			$("#amount").val(ui.value);
		},
	});
  
  $("#amount").val($("#slider-vertical").slider("value"));
  
  // Get Response
	$('#slider-vertical').on('slide', getResponse);
	// this won't work: getResponse(0);

	function getResponse(e, ui) {
		//let itemlevel2 = $("#slider-vertical").slider("value");
    let itemlevel2 = ui.value;
    console.log(itemlevel2)

		ajaxManager.add({
			type: "GET",
			cache: "true",
			url: "https://elder-scrolls-online.eu/datenbank/itemscript.php",
			data: {
				"itemlevel": itemlevel2
			},
			success: function (data) {

			}
		});
	}
});