The reviewer only has the option to comment and @ someone if they want another person to review the invoice as well.
Since users can only access invoices where they have been mentioned via email notifications and not via their inbox, these mentions are often forgotten. Which forces AP users to send it out for review again and act as the middle man. This leads to invoices taking an unnecessary amount of time and manual handling before they are ready for payment.

Users need to be able to communicate with eachother efficiently in Medius without needing us to do it manually for them.