You can see the invoice in Accounting > Invoice. You could select Awaiting, to see outstanding invoices or Paid, paid invoices. There are 2 ways invoice is generated automatically :
1. In Sales, after enrolling the student in a course and saved, but not check out.
2. After enrolling in a class, in the mid-month, the invoice will be generated for next month automatically.
The invoice is grouped by billing month automatically. For example :
1. If there is an order of Sept class and another order of Oct class, it will be separated into two invoices automatically for your easy reference.
2. If there are 2 orders with Sept class, they will be grouped into one invoice.
3. If the order contains Sept and Oct classes at the same time, it will be classified as Sept invoice.