Not putting https:// in a link will append the added link to knowledge base domain.
It's not innate that you HAVE to include an https:// in order for an external link to work.
When you leave it off, it simply appends the link you've inputed to your portal domain, causing a 404.
Either revise this functionality so you can include links without https:// or let people know in an inline description that you need to include an https://
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