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Root domain

You need to set a wildcard root_domain on the store to enable multi-store setup 
Spree.root_domain = ENV.fetch('SPREE_ROOT_DOMAIN', 'lvh.me')
This will be used to generate the store URLs, eg. store1.lvh.me, store2.lvh.me, etc. store1 part is the unique store code identifier, which is auto-generated based on the store name. You can change it in the admin panel in Settings -> Domains.
If you later change the root_domain, you will need to run:
Spree::Store.all.each(&:save)
to update the store URLs.

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Creating new stores

After you restart your application, you will see a new option in the admin panel, under new item menu: You can also create a new store from the rails console: 
Spree::Store.create!(name: 'New Store')
This will create a new store with the given name, code and URL.