Review the information that's been provided. Do you have everything you need to complete the purchase (for example, the shipping costs, and amount of any additional fees)?
Include a message to the seller asking for the information you're missing.
Click the Request Total button. eBay will email your shipping address and message to the seller, and will ask the seller to provide you with the information you need.
Wait for the seller to email you with the information, then complete your purchase.