'Cash from debtors' means any income you receive from clients that you send an invoice to, usually during the course of and at the end of a project. After they have been sent an invoice but before they pay, they are your debtors. When they pay you, the payment is referred to as Cash from debtors.
Because a project can take many months between the initial commission and completion, it is advisable wherever possible to agree stage payments or monthly payments with your clients. These fees may also include disbursements that you have paid on your client's behalf.
Make sure that any program of instalment payments which you have agreed with your client is clearly set out in the formal document that you draw up when you are appointed.
You'll need to make an estimate of the income you might receive from debtors and enter that amount in the month in which the money will be received.