Here is how you can record the dues of the customer:
Step 1: Click on 'Menu' on upper left corner
Step 2: Click on 'Customers Management'
Step 3: Click on the customer name of whom you want to record the due amount
Step 4: Click on 'View Profile'
Step 5: Click on 'Return Amount'
Step 6: Enter the due amount, choose the method of payment and click on 'Return amount'
Note: Click on send SMS to send SMS to the customer
Related articles:
How to record the advance received from the customer?
How to reset the due of customer?
How to see the transaction history of a customer who are added to customer management?
How to see the order placed by customers(after billing) in customer management?