Why does it say Easy MTD VAT is not a Microsoft-verified app when I try to install it?

The reason a "The app you're trying to install isn't a Microsoft-verified app" window is appearing when you try to install Easy MTD VAT is because Windows is in S mode.

Windows S mode only allows applications from the Microsoft Store to be installed. Easy MTD VAT is not one of those applications. However, you can turn S mode off so you can install applications outside of the Microsoft Store. Click here for instructions about how to do this.

When the above actions have been performed you can install Easy MTD VAT in the normal way.