I'm so sorry but we have to remove the free postage for add ons. It's being used as a normal postage option more than people using it for adding an extra item or 2 that they forgot.
This means every day we're cancelling and refunding orders. If only it was used for the reason it was put there, we tried to state as clearly as possible what that free postage option was for but I think people see the 'free' and automatically click it without reading.
If you're a regular customer please get in touch and we can still add on an item if you're desperate but there is no option to add on for free as from today ...