How do I amend postage charge on invoice

[stampsbuyer]

Hi, I buyer from Ireland asked about cobining postage if he bought a number of items, I told him to proceed with the order but not pay and I would adjust the invoice. He did that but the invoice doesn't show any charge for postage and I don't have the option to amend the invoice, it isn't available on the list of options. He is happy to pay the shipping but I'm not able to add it to the invoice. How can I charge him?

Thanks for any help

[profgaz]

Via a web browser, Not the App.

Go to the right drop down menu of an item > Choose Send Payment Details,
Items should appear on one invoice.
Amend postage but don't click reset.
Check invoice then send.

(Must Not be enrolled in eBays GSP to do above)