Your Domain is the primary domain on your Shopify store. If you haven't added a domain name yet it will be *.myshopify.com.
You can add or change your domain via your Store admin:
Shopify Article on adding a domain to your store:
If you add or change your primary domain on your Shopify store it will automatically update in the Cardzware Control Panel.
Bear in mind if you change your domain to a new one you will need to set up a new subdomain in your Cardzware account and with your domain provider.
To set up a new subdomain with Cardzware go to: