Add-on orders can be used to add extra items to an order after the original order has been placed. Add-ons are chargeable to your customers. (Remedials are for additions that are not chargeable).
You can create an add on order from right-clicking on the original order reference.
1.Locate your order in the Customer screen or the Projects screen.
2.Right-click the order reference number and select Create… > Create Add-on
3.Answer Yes to the Create Add On order question.
4.A new blank remedial is created with a new reference number. Remedials can have a suffix added to the reference number. See auto numbering setup.
The add on order opens at a blank screen. Press 
Edit at the bottom left.
5.To help identify this order you can enter an Own Ref at the top.
6.You can continue to work with the remedial order as you would with a full order. Add and remove products in the same way as a full order using the Add Product button.
7.Repeat as necessary to add more products. Continue to work with the order as a normal order.
When you are finished with the order click 
Save on the bottom toolbar. You can then click Print.
To access add on orders for viewing/editing, they are stored in the sales order tab with full orders. Right-click the reference number to open, place orders etc.