This is very common with pixel tracking codes. The head section (<head>) does not accept any code that is <img>, <iframe>, and more. It normally only takes <link>, <script> and <meta>.
If you have to paste code that's not being saved in the head section, paste it in the header or in the body-end.html. To do so, follow these steps:
Placing code in the header:
- In the side panel, click Settings and then click Head HTML.
- Paste your code in the Head HTML section and click Save.
Placing code in the body-end.html:
- Click the Developer Mode () icon in the navigation bar.
- Click Site HTML/CSS.
- Select body-end.html.
- Past your code into the last line.
- Click Save.