2 weeks ago
You should be able to select send invoice, select all items to be combined and adjust postage cost.
Don't click recalculate.
If it is because eBay has automatically changed your listings to Immediate Payment Required buyers need to place items in the cart first then request total. But the cart has also had issues.
You could try to untick the option for IPR on your listings if that is a preference for you.
(I haven't personally tried that via the bulk edit option but think it should be possible)