You can create an additional fee by creating a price trigger based on order type.
As soon as "Delivery" is selected as the order type on the POS, a fee will be added to the order.
Delivery fee (based on order type)
1. Go to Sales > Price Triggers
2. Click New Price Trigger
3. Enter the name of your price trigger, eg. delivery fee
4. Click the pencil button to go to the Price Trigger Details
5. Ensure that Run Type is set to Run Once
6. Under Order Type, select Delivery
7. Click Save
8. Perform a Master Sync on Abacus POS.