If you are using Server version of Confluence, please refer to How to install Inspire Server
Only members of the Site-Admin Group can add Paid Add-ons or Applications to the instance
By using Confluence Apps Manager
Navigates to the "Find new apps" section in the Confluence administration.
Type "Inspire for Confluence" into the search field and hit the Enter key.
Click app to view the details.
On the app detail view, click on the Get app button.
Click on the Get it now button in the new pop-up.
When completed, a Success popup will show on the top-right corner to inform you that the app has been successfully added.
By using the Atlassian Marketplace listing
Open the Atlassian Marketplace and search for "Inspire for Confluence".
Click app to view the details
On the app detail view, click on the Get it now button.
A pop-up will appear asking you to Choose a site to install your app.
You will be redirected to the "Find new apps" page on the site and a pop-up will appear.
Click on the Get it now button in the new pop-up.
When completed, a Success popup will show on the top-right corner to inform you that the app has been successfully added.