I am very visible throughout the site, and it's very frustrating that I can sign up for a profile using Facebook sign-in, but can't use it to perform admin functions. I already signed up via Facebook so I now have two profiles, but only one useable one.
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Hey,
At the moment we don't support this feature. If you want to sign in as admin, you need to log in with the same email and password as you are using for Wix.com. We will add this feature request to our wishlist. Thanks!