The error message is gone now but one is directed to the Unifi index page instead.
Where I cannot find the option to check for the Turbo Upgrade.
My advice to TM/Unifi would be:
Don't post promises/statements before you have ensured that they are valid!
We have received some info that the website to check upgrading eligibility is down at this moment.
As expected due to the overwhelming response.
Stay Cool! Once up people will announce it.