11If you have not setup primary domain for your Shopify store or not redirecting all traffic from all other domains to primary domain, API does not return the name of custom domain.

To fix the issue,  Click Here. (If prompting you to login, use your Store Admin Login details)

Have a look at below given screenshot. Try to match it with your settings and apply the fix if needed. 

This fix is required for 2 of our apps.  1 - Google Trusted Store App and 2 - Bing Shopping Feed App. 

This fix is must from SEO point of view as it avoids duplicate content (due to same content loading from different domains) getting into Google's Index.