Next to one of the items on your selling page should be a blue button to send an invoice. If it's not there, look in the dropdown to the right of the item. When you click on it, it will open the invoice page. All the items that buyer has bought should be there. Change the postage cost to the amount you wish to combine to and then send the invoice. DO NOT hit the recalculate button as that reverts it back to the original amount. Just hit the send button down the bottom left.
