Hello,
As previous comments stated, this is an IP issue, which I tested and found it's a result of accessing the service from outside the UK. Personally, I'm in Australia and received the error which I resolved by using a VPN with the region set to UK. My best guess is someone decided the browser service should be unaccessible outside the UK as a security measure, which is somewhat justifiable.
My recommendation for a temporary fix is to use a VPN like windscribe and set it to a location in the UK. For a permanent fix, especially if you have no plans of returning to live in the UK, create a gmail account or use an existing one from now on. Go to all your accounts using the Sky email and have them switched to gmail(except junk mail services). If you dislike gmail for any reason, my next recommended email service would be outlook.
