In some cases, the Atlassian app might not be available via Atlassian Marketplace.

Some possible situations: app early access, QA/Staging/pre-production environment, troubleshooting session.

To install the app you must be in the administrator group.

Manage apps
Top menu bar > 'Apps' > 'Manage your apps'
Settings  Enable private listings
Settings > Enable private listings > Apply

Important: reload the page!

After page reload you will see the “Upload app” button that looks like a link.

Upload app
Upload app > enter app url > Upload

Done. App should be installed.