If you have Immediate Payment Required on any of the listings, you would have to turn it off. Since "Request a total" from one's Cart requires the buyer to commit to buying all the items it would end the listing (if single item listings; for multiple item listings it would reduce the inventory and possibly end if s/he commits to all your current inventory and you have your options set to end the listing in that case) which when you enable IPR you have instructed eBay to not allow. (Where eBay is requiring the immediate payment instead of the seller it would not go against the stated sellers wishes to do that so it is allowed unless the seller set IPR).
