@arsenalcomics, I don't know if you have resolved this yet or not, but for the record, this is what caused the problem:
Those listings have different options for international shipping. The two listings that were removed from the invoice have the Global Shipping Program, and the two listings that stayed on the invoice have "USPS First Class Mail International / First Class Package International Service".
You can't send an invoice for items with GSP shipping, so that explains why they were removed from the invoice. I presume that the buyer wants to pay for them all together, but it may not be possible for that to happen.
It used to be that, if the buyer sent a request for an invoice for a GSP item, then the seller could send an invoice and that would take the item out of the GSP. I don't know if that still works or not. eBay doesn't always allow a buyer to request an invoice from the checkout page. I have run into this myself as a buyer, and sometimes they were international purchases, but I haven't been able to identify exactly why I couldn't request an invoice because the sellers didn't answer when I asked about it.
If you have received an email from eBay (not just a message from the buyer) saying that the buyer requested an invoice with the combined total, and you still can't send an invoice, then I don't think there's any other way to combine them.
If not, then ask the buyer to send you a request for invoice by using the link on the checkout page. If he is able to do that, then you may be able to combine them and send an invoice for USPS shipping for all of them.
There's no way to add the 2 with USPS shipping to the GSP invoice, which is currently showing cheaper shipping than the USPS international shipping for the less expensive comic because it is below the threshold for import duties. However, the expensive one does have import duties, and if they are combined then the entire purchase would be subject to import duties I believe. However, if the package is shipped through the post office, sometimes they waive the import duties even when they are due.
If the buyer doesn't want to use GSP shipping, and you can't get those 2 out of the GSP, then you would have to cancel the transactions and relist them with USPS shipping so the buyer can purchase them again. I would recommend that you coordinate with the buyer and make sure they understand and agree to this, and will be available to purchase them immediately. Then relist as fixed price with best offer, have the buyer submit an offer for the amount of their winning bid, and then accept the offer so that they can pay the same price.
