Tik Tok
Step 1
Install this code in the first line of the index.php file:
CODE
<?php if(isset($_GET['ttpixel'])) { setcookie('ttpixel',$_GET['ttpixel'],time()+36000); }; ?>

Step 2
In the success.php file, set the pixel code before the </head> burrowing tag..
CODE
<!-- TikTok Pixel Code Start -->
<script>
!function (w, d, t) {
w.TiktokAnalyticsObject=t;var ttq=w[t]=w[t]||[];ttq.methods=["page","track","identify","instances","debug","on","off","once","ready","alias","group","enableCookie","disableCookie"],ttq.setAndDefer=function(t,e){t[e]=function(){t.push([e].concat(Array.prototype.slice.call(arguments,0)))}};for(var i=0;i<ttq.methods.length;i++)ttq.setAndDefer(ttq,ttq.methods[i]);ttq.instance=function(t){for(var e=ttq._i[t]||[],n=0;n<ttq.methods.length;n++)ttq.setAndDefer(e,ttq.methods[n]);return e},ttq.load=function(e,n){var i="https://analytics.tiktok.com/i18n/pixel/events.js";ttq._i=ttq._i||{},ttq._i[e]=[],ttq._i[e]._u=i,ttq._t=ttq._t||{},ttq._t[e]=+new Date,ttq._o=ttq._o||{},ttq._o[e]=n||{};var o=document.createElement("script");o.type="text/javascript",o.async=!0,o.src=i+"?sdkid="+e+"&lib="+t;var a=document.getElementsByTagName("script")[0];a.parentNode.insertBefore(o,a)};
ttq.load('<?php echo $_COOKIE["ttpixel"];?>');
ttq.page();
}(window, document, 'ttq');
</script>
<!-- TikTok Pixel Code End -->

For the code to work correctly, you need to write ttpixel=value in the link.
Example: https://app.limonad.com?ttpixel=CBL3SKJC77SFJ