Hello Mark,
Domain has to match your "unsecure/base_url" for your default config. Go to configuration System/Configuration/General/Web in Magento Admin and check Base Url settings for Default Config (see screenshot).
If you base url is correct make sure that your server is able to send the requests to another servers (the checking is doing remotely).
If you found that is all right, but M-Turbo still does not work, send your download id and your domain to me at
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I would check your credentials again our database.