For security reasons Opigno LMS using a private file system to check if a user has related permission to download a particular file. For example, answers for "Opigno file upload" activity type should be accessible only for users who create these answers and users with global role "Content manager" etc.

The private files system is not configured out of the box so need to be done these steps to configure it:

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-file

To manage the allowed extensions for the "File upload" activity, you will have to edit these 2 config files:

modules/opigno/opigno_module/ActivityTypes/opigno_file_upload/config/optional/field.field.opigno_answer.opigno_file_upload.opigno_file.yml
modules/opigno/opigno_module/ActivityTypes/opigno_file_upload/config/optional/field.field.opigno_activity.opigno_file_upload.opigno_allowed_extension.yml

and then re-import them (at /admin/config/development/configuration/single/import)

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