It was working fine, and somehow, it just stopped working.
Solution:
Login to the backend of ExpressionEngine
Then go to Add-Ons – Modules –
../admin.php?S=0&D=cp&C=addons_modules
Click on Zoo Visitor
Then Go to installation ยป click the button at the bottom to Reinstall Everything.
Once the Zoo Visitor is installed, you do not need to change it, the installation makes sure everything is in place to just start. The default Guest member is necessary to accept registrations.