In some cases, when pressing a link to Knowly in a desktop email client such as Outlook, certain characters are added to or removed from the link. Since every link is unique, this means that the link is no longer readable and you end up at an error page.
Option 1: Right click on the link or button in the email and select "Copy link address".
Now open Google Chrome (not Internet Explorer), paste the link in the address field and hit enter.
Option 2: If you have access to the email on your smartphone, instead open it there, and you should have no issues.