You need to register you account to be able to use it. Do it here:  https://www.nutanix.com/products/community-edition/register

Hi Joshua,

I’ve already a MyNutanix and Next-Account, both with the same mailaddress. If I try to activate the community edition (followed your link), ill get the response, that my mynutanix-Account seems to be not activated. But im just able to login to my mynutanix account.

If I Login to my Next-Account on my Nutanix-CE Server, ill get the Response:

Your .NEXT account does not have the required Community Edition. role. Please request the role from your Nutanix contact or on the .NEXT forum

Looks like you should chime in here:
https://next.nutanix.com/discussion-forum-14/community-edition-activation-44173