When approving your invoices, you have the option of not emailing them to your customers
For a customer to have an outstanding debt with you, they would need to have an approved invoice on your account. This is how Class Manager knows that they owe you some money.
However; there may be an instance where you want these to be approved but not actually be emailed to your customers. Perhaps, for example, if you take 'Pay as you go' payments from them and do not want them to receive an invoice but still have a debt with you.
To do this, you would just need to generate your invoices as normal so that they appear in the 'Draft' status.
Then you would use the same option that you would if you were sending them to your customers. So 'Select All' (or select your required invoices) and under 'Group Actions', click 'Approve'.
This will redirect you to the page where you input your due date for these invoices. On the left, there is a tick box that says 'Email Invoice(s) to the customer'. This is ticked by default. But if you do not want these invoices to be sent simply untick the box.
Then click 'Approve' as normal. This will mean their invoice will show as 'Awaiting Payment' and they will now have an outstanding debt with you, but they will not have received the invoice themselves.