Ebay shipping has been having problems as is USPS.
Make sure the address format is correct by checking it here:
https://tools.usps.com/zip-code-lookup.htm?byaddress
Unless you qualify for the extra top rated discount the cost is the same at paypal.com/shipnow
As a great backup open a free Pirate Ship account, it will import directly from ebay and has all the options available for USPS and UPS at discount.
