If you need to cancel a transaction on the network so that the commission will not be paid out, you will need to go into your account, under the reporting tab, to Check Transactions > Transactions.
Locate the transaction(s) which are invalid either by transaction reference or selecting the date range of the transaction, and select the "cancel" button under the 'Action' column. The next page will take you to a drop down menu from which you can select the reason for cancellation.
Please note that the cancellation reason will go back to the affiliate, so ensure that the reason is relevant and informative.
You need to ensure you check your transactions within your set cancellation period, and cancel any necessary transactions within this time frame. After this period, the transactions are locked. If you are unsure of your network cancellation period, or would like to enquire about changing it, please contact the support team or raise a ticket.