By default your storefront’s subdomain is your eBay user ID (eBayUserID.webstoreplace.com) but you can also change it in your control panel.
If you changed it and are not sure what it is, or you want to change it follow these steps:
1. Login to your control panel using your eBay login info: http://www.webstoreplace.com/site/login
2. Under your main tab, the “Address” tab, you will be able to see your current subdomain. By clicking on it you will be directed to your storefront.
3. To change your subdomain simply enter a new subdomain in the given field. Make sure that it doesn't contain any special characters and only contains numbers and letters.
If you have any other questions feel free to leave a comment here below.