You generally cannot add a Buy Now price to a live auction if it has already received bids that meet the reserve.
Enter a Start Price and an optional Reserve Price . You will then see an optional Buy Now field. Enter the fixed price at which you are willing to sell the item immediately.
To add a price to your Trade Me listing, you can either include it while creating a new auction or add it to an existing live auction that hasn't met its reserve. Adding Buy Now to a New Listing