To see the information about ActivityTimeline license, update license key or buy a license, administrator should go to Configuration > License.
In the opened License page see the contact information, your Installation ID, current License Key, evaluation period end date (if you are currently evaluating ActivityTimeline add-on).
Starting from July 2020 ActivityTimeline can only be purchased through Atlassian Marketplace as an Jira internal add-on.
Please check the following page for more information: https://activitytimeline.atlassian.net/wiki/spaces/AC/pages/1603502105
You can still purchase a renewal of the legacy version via the following link: https://activitytimeline.com/buy-license-renewal.html
Edit License Key
To edit existing license key click Edit Key link. The system will redirect an admin to License Update page where new license key can be entered and updated: