If you have credit, which you can check on the 'Referrals Dashboard' or by clicking your profile picture in the top right corner, it will automatically be applied to your next lesson that is part of a regular booking.
Credit can only be used on the first lesson since receiving it. Unused credit does not carry over to the next lesson.
For credit to automatically apply it must be used on a recurring lesson.
One credit token can only be used for one Sherpa lesson.