External Access to Sharepoint Problem

Apologies, I am not technical and I am struggling to solve an issue with an external user that I am trying to grant access to a folder.  They get the link and are shown as sharing on the file but they can't gain access without a password.  This is not a condition that I have set?

This whole experience has been a bit of a nightmare, if I were techie then I have the feeling I would understand the advice and could solve the issue, but nothing seems written in plain english for a lay person!