It may be difficult to get payment for an item sent out without the Buyer making payment.
You could contact eBay's CS that deals with Simple Delivery to see what they suggest.
My relative uses Simple Delivery on her Private account
- eBay adds the postage to her advert plus the Buyer's Fees
- if a Buyer purchases a few items on one transaction, she leaves it up to eBay to combined postage that includes insurance cover if purchased on one transaction, so the Buyer can pay for the postage label.