What is the difference between a monthly pack and a credit pack?

A monthly pack recurs: its session quota belongs to the running period, its invoice is issued on the school's issue date, and unused sessions do not roll over into the next month. A credit pack is bought up front for a number of sessions, used until it is empty, and is not renewed automatically.

Credit applies in the class the pack was sold for, so a student in two classes holds a pack for each — and a balance in one class is never quietly spent by the other. For a course whose session count is fixed, the class is set as fixed-session and the pack is born exactly that size.