You cannot display a lot of websites inside an iFrame. Reason being that they send an “X-Frame-Options: SAMEORIGIN” response header. This option prevents the browser from displaying iFrames that are not hosted on the same domain as the parent page.
I faced the same error when displaying YouTube links. For example:
https://www.youtube.com/watch?v=8WkuChVeL0s
I replaced watch?v= with embed/ so the valid link will be: