Bundle a month of tier subscription, overage and flat or per-class fees into one invoice, send it, and track payment.
The page is titled "Instructor invoices". Pick the month you are billing at the top.
Click "Generate for all instructors". Klasly creates one draft per instructor from that month's tier subscription, overage, and flat or per-class fees, and tells you how many it generated and how many it skipped.
Use "Apply code" on a draft row to attach a discount code. The redemption is recorded when you send, not when you apply.
Click "Send". The instructor gets an email with a "Pay invoice online" link, and can pay by card from their own Invoices page.
Once sent, the row offers "Mark paid" for money that arrived outside Klasly. "Void" cancels an invoice you no longer want to collect.