For US sellers, combined international shipping may no longer be possible if using eBay's new international shipping service.
eBay's new international shipping service for US sellers specifically prohibits US sellers from combining shipping for sales to be sent internationally.
Here's what eBay says:
"Combined shipping is currently not available through eBay International Shipping. Please ensure all items in a single order are packaged together for shipping and properly identified for export and import. Do not combine items from several orders even if both are for the same buyer."
Here's where that comes from: