Why is user registration currently not allowed?
On a fresh WordPress install, registration is disabled by default. When a user tries to register on your site, they will be met with the following message: "User registration is currently not allowed." In order to enable registration, visit your WordPress Dashboard, and go to Settings → General.
From there, you'll find a setting labeled "Membership" with a checkbox next to it labelled "Anyone can register".
Check this box and then click the "Save Changes" button at the bottom of the page.
Congratulations! Registration is now enabled on your site!