Before Information Rights Management can be used on any document, library, or list item, it must be enabled. To activate IRM, follow these steps:

1. Navigate to the SharePoint Admin Center (https://admin.microsoft.com | Admin centers | SharePoint).
2. Select Settings and select Classic settings page.

3. Scroll to Information Rights Management (IRM), select Use the IRM service specified in your configuration, and then click the Refresh IRM Settings button:

4. Scroll to the bottom of the page and click OK.
5. Close the Classic settings page. 

It may take up to an hour for the IRM settings to be available for lists and libraries.