WordPress

There are two easy ways. The plugin way survives theme updates, so start with that.

With a header plugin (recommended)

1. In WordPress go to Plugins → Add New and install a header and footer code plugin, for example WPCode.

2. Open the plugin's Header box.

3. Paste:

   <script defer data-site-id="YOUR-SITE-ID" src="https://spintaxifycms.com/js/analytics.js"></script>
   

4. Save.

In your theme

1. Go to Appearance → Theme File Editor and open header.php of your child theme.
2. Paste the line just above the closing head tag and save.

Use a child theme, otherwise a theme update removes the line.

Note: caching plugins may keep serving the old pages for a while. Clear the cache once after adding the line.

Check it works

Open your site in a normal browser window (not one where you are logged in as admin, if you excluded admin pages). Then open Analytics in Spintaxify. Within a few seconds Online now shows 1, and the setup card ticks Install the script.

Tip: your site ID is in Analytics → Settings → General. Copy the snippet from there and it is already filled in.