This issue occurs when the access token has expired. After receiving the email, the link is only valid for 24 hours.
If you open the link at a later time, it will no longer be valid. In this case, you will need to log in directly via the Mobility Manager and then request a new validation email using the provided link. You should receive the new email shortly and confirm the link within 24 hours.
Note: You can log in by clicking on the human silhouette in the top right corner and entering your account information. After logging in, you should find a link to request a new email validation link.