To request a final invoice for revised postage costs: via mobile or app you need to commit to buy each item separately by selecting buy it now and then send me a message when you have finished shopping and I will then send a new invoice. For desktop versions the option is available on the payment page under contact seller menu in the shopping basket. If you pay in full before requesting an invoice I will always refund any overpaid postage but it will be minus any fees charged by Ebay.