WordPress

Without a plugin. In your theme, open Appearance, Theme File Editor, and paste the snippet into header.php before </head>. This is lost when the theme updates, so prefer a child theme or the plugin route.

With a plugin. Install "WPCode" or "Insert Headers and Footers", open its settings, and paste the snippet into the Header box:

<script src="https://replaycat.com/rc.js" data-site="YOUR_SITE_KEY" async></script>

Some header plugins strip attributes the way GTM does. If the Install page never shows "receiving events", switch to the URL form:

<script src="https://replaycat.com/rc.js?site=YOUR_SITE_KEY"></script>

WooCommerce checkout fields are inputs, so they are masked automatically. Mask order totals with data-rc-mask if you do not want them in recordings.