For privacy reasons we try to hide the fact whether a link has or has ever existed. When we don't find a link, the default error message is This link has expired.
Many times this means the link might have been copy-pasted incorrectly. When emailing or sending links, there's a risk of accidentally removing or changing some characters.
Example: Your link might look like this:
https://participate.lookback.io/s4HYex
If you by accident remove or change any of the last letters s4HYex, the result will be the error page.