Get an app password for two-step verification If you can, open an application like Word and click Help > Check for Product updates. In many cases, updating Office will fix the problem. In the Get Started wizard, click Sign in to an existing Microsoft 365 subscription, and sign in with the email address that’s associated with Office. Open an Office application and click Activate Now. Instead, sign in with the email address that’s associated with Office. If you have a Microsoft 365 subscription, you can’t use your product key to activate Mac 2011. Sign in with a Microsoft 365 subscription If you’re getting an invalid product key error, try these solutions.