"Only a class card can be renewed."

Where: Renew the card on the student profile, or Renew in the Over plan list (owner).

Why: only a class card can be renewed. A monthly subscription continues on its own every month until its end date, if it has one.

What to do: for an ended monthly subscription, Edit its end date (or clear it) or Add a subscription. For more attendances in a given month, use the This month row.