There is a technical issue for Private sellers not being able to currently, offer combined postage. Sellers are trying every which way to help buyers, seems this seller has sent you a separate Invoice ? Not sure how.
In your Purchase History are the items there and to the right for each a ' Pay Now'. ? Then, it is advisable to pay there which takes you to eBay checkout. Do so if you agree to 3 postage charges as the seller is not obliged to post the items together and may wish to send them separately so ensuring a tracking number for each item, this when showing delivery releases their payout sooner.
You will have to message the seller explain what you have found and the issues, the easiest workaround would be for the seller to cancel all items, citing Buyer requests to cancel, this then doesn't affect their account, list them together for you to buy as one item. Making sure any messages sent to you , make it clear the cancelling is for the items to be listed again, on eBay, for you to buy.
@marksman19710035
