You can share an invitation link or a QR code to your course or stream through the Manage Learners 
feature, you can manually set its expiration date.
NOTE: Every time you enter the Manage Learners menu, the platform generates a new invitation link and QR code that you can send directly to your learners.
Link has expired - Learners who click on this link after its expiry will receive this page and will not be able to join your course/stream.
If you wish to allow, these learners to join your course/stream, create a new link with new expiry settings and send it to them.