Sorry not to reply very asap, I have only just seen your post when I logged on this morning.
If the buyer hasn't paid, then you can send them a revised invoice:
Go right of the item sold to More Actions, and select Send payment Details, amend the postage there to that required, but do not click on reset. Check it is correct, and send .
If you are on the Seller Hub, you click on the item in Orders >> Awaiting Payment, then top left you will see send Invoice, follow the above instructions.
You may need a PC / laptop and not the app or mobille browser to do this, Chrome and Firefox work well with eBay.
If they have paid you then need to do a partial refund.
@stubul92
