Switchy uses iframe technology to load web pages and add embed script or widget on it.
For security purposes, some websites are blocking iframes. Embed scripts or widgets can't be added to those.
For example, banking portals and payment processing sites like PayPal are not supporting iframes. Also, some big e-commerce websites (like Amazon or Zalando for example), do not allow to iframe their pages. On the other hand, there are huge informative websites (like for example The Economist, or Mashable) that allow iframing their content.
For your information, nearly 3% of the most popular websites do not allow the iframe embed option. For the rest, let your creativity express itself! 🧙♂️
💡 Tip: In order to check if a website allows iframes, you can try to add it directly in the Embed widget page, by clicking on the eye icon of one of your embed widget.