To be able to add a negative amount on the deduction $ field, user need to enable the allow negatives feature in darwin Cloud first. Please see the steps below for your reference:

1. Click Formulas menu
2. Click Deduct types submenu
3. Check (✓) the deduct type under the allow negatives column
4. Click save

Enabling this feature will now allow the users to add a negative amount (credit) to the Agent Net List/Sell deduction field in the Properties menu.