To add optional fields in your invoices in BUSY, you need to follow these steps:
Step 1: Go to Administration and click on Configuration.
Step 2: Select Voucher Series Configuration and choose the voucher type such Sales, Purchase, etc.
Step 3: Select the series and click on Voucher Configuration.
Step 4: Mention the No of optional field as 1 and configure it with the field name as Pending Amount, then save.
Now, when you create invoice you need to manualy enter the amount in it, no feed automatically the pending amount.