How do I go about closing my course to new sign ups, without closing access to those already enrolled?
You can go to Dashboard > Course > Pricing and delete the price from your course. It will keep students who are already enrolled in the program, but not allow any new sign ups.
The standard message you will see at the bottom is “This course is not open for enrollment”. You can change this wording in Admin>Site> Custom Text
You might also delete the pricing block on the sales page to remove the message completely.
Note: If it’s a monthly or yearly subscription, deleting the price will not delete their subscription. It just stops new people from signing up. You might want to add in a Rich Text field on the course sales page that reflects the original price of the course, without “buy now” links.