Thanks for using Apple Support Communities. Select the product youd like to install, click Install and. If you need more help with activating Microsoft Office 365, reach out to Microsoft using the 'contact us' link at the bottom of that website. You should now be able to access and manage your Microsoft 365 products and subscriptions. You should be able to view more information about all of this here: Microsoft - Office install. As you'll see in the description section of the Microsoft Office 365 app in the Mac App Store, Office 365 offers annual subscriptions that can be billed to your App Store account. According to the Microsoft website, once you purchase Office you should be provided with a product key you can use to activate Office on your Mac. Have you purchased a copy of Office 365 previously? Although the apps that come with Microsoft Office 365 (i.e., Word, Excel, PowerPoint, and Outlook) are free to download from the Mac App Store, you may have to purchase Office in order to activate them before you're able to use them. I'm happy to help you sort this out so you can start using that app the way you expected to. If I'm understanding you right, you're being asking to verify your license when using the Office 365 app that you downloaded from the Mac App Store.