Error Authentication

Keycloak instance = Keycloak.getInstance(“http://0.0.0.0:8080/”, “myrealm”, “user”, “user_password”,“client_id”, “client_secret”); TokenManager tokenmanager = instance.tokenManager(); String accessToken = tokenmanager.getAccessTokenString();
i want to return the token but it does not i don’t no where problem is coming from? do you have an idea?