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- If you have already installed Opigno LMS instance go to admin/reports/status and make sure there are no related errors or warnings. In addition, you should see "Private file system path is set" for requirement "Private Files System". If you don't see this message see next step.
- How to set a private system path: https://www.drupal.org/docs/8/core/modules/file/overview#content-accessing-private-files