Video doesn't belong to this course. Contact vendor to get video of your course.
Player app doesn’t have full permission to access storage and phone memory etc. Provide full access to App and try.
Internet speed issue. Change internet connection, use broadband with bit higher speed. Do not use data connection for internet.
Either internet speed is slow or server is not running. Change the internet connection to better speed or ask vendor to check the server.
Phone is old and doesn’t support Player App. Contact vendor to get old player.