A voucher lowers an invoice. A lesson package counts lessons. The exam stays at full price.
Under Work or on the student: a gift voucher or a promo voucher. The gift voucher applies once its invoice is paid. The promo voucher applies immediately. You can scan the code and limit it to one course.
First the lesson package in the catalog, then on the student. It counts lessons in the chosen categories from the sale on. Lessons from before stay out unless you select them. On the student account the student sees the remaining lessons. You can show the amount instead, or hide it.
Redeeming is its own step, on the person who has the code. The first name does not lock the code.