Why can’t I combine items sold to send invoice?

[bosstone33punk]

The seller has purchased 2 items and I’m trying to combine an invoice with new shipping amount but keep getting this message? Shipping on my items was Royal Mail not eBay postage 

 

[**peaseblossom**]

You have ebay's Simple Delivery on your listings and combining postage isn't working with SD at the moment.   You have to either send each item separately, or cancel/refund the transactions with buyer agreement and relist with the items all on one listing with one postage for the buyer to buy and pay again.