The first error is due to the client_id you are trying to login into has no connections enabled. If you open up the application in your tenant dashboard (Applications > Applications on the left hand side), there is a tab for connections, here you can toggle on connections you wish the client to use, such as an Auth0 database or Social Login like Google with OAuth2.
The second error is because the verification link is a single use link, it may have been double clicked, or you have an email scanner that is issuing a GET to the page before you can click on it, but the first time that link was used it should have successfully verified the email.