Try this, but use a laptop / PC not the app or mobile browser and try Chrome.
Then, go right of the item sold to More Actions, and select Send payment Details, amend the International 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.
@catscoobie
