This issue is not relevant to the Office 365 Add-in.
Error message “login.vevox.com uses an invalid security certificate” when logging into the Add-in in PowerPoint.
If you see the below error message when trying to log into the Vevox PowerPoint Add-In, please update to the latest version of the Add-in.
You can download the latest version of the Add-in from this link.
Or alternatively you can do this through PowerPoint under VEVOX > Help > Check for updates.