Which web links can I insert?

All external web links that are valid: An external weblink is only considered valid if it starts with "http://", "https://" or "mailto": e.g. the homepage, an event stand, an Amazon product, a landing page with embedded tracking code.

Please note that this web link must point to a publicly accessible website. Otherwise, users will not be able to access the website.

More information on this topic in this blog article.