When attempting to add your domain to your store and the following error appears:
"A store with that domain name already exists.”
This error indicates the domain may have set up on another store.
For example, you may have signed up in the past, added a domain to your store, closed your Shopify account but forget to remove your domain.
To resolve this situation you’ll need to contact Shopify Support with the following details:
After gathering this information contact Shopify Support via email, or phone using the contact details listed on this page here so the team can help you out. If you have any questions about this please submit a new topic providing as much detail as possible so the team can assist.