The client does not have a secret configured. If you are the client application developer, configure a secret through the application management site at Microsoft Azure.
We started getting this message a few hours ago. We’ve been using the free level of auth0 for over a year. Nothing was changed on our end. Looking at the App Registration, we don’t see any secrets configured for it even though a value appears to be configured in the Auth0 setup. Is this the problem? We’re trying to locate an App Owner who can add a new secret but meanwhile no one login to the our app.