To check your Course Request setup, navigate to:

onRecord > Settings > Course Request Setup
Select the School Year from the dropdown
Towards the top, you will see a Header for: Exceptions To Communicate there are the following options:
  • Has already taken the course
  • Lacks prerequisite
  • Assigned to a different grade level than the course
You can select the following choices within the above options:
Show message to display a message to the student (Note: The system does not lock the Course down and the Student can still select the Course.)
Hide course from list to hide requests from the Student
Ignore to Ignore and not communicate to the Student