Hi @armida.rehanyan ,
Auth0, as an email provider, is for testing purposes only. -Ref
On the Auth0 side, there are no limitations in terms of what email account (gmail/yahoo/other) a user is using.
Another thing you can verify is if the Username-Password connection you are referring to has the sign-up option disabled (please see the screen below). If so, please ensure the user with a Yahoo email is added to a connection.
If the affected user has more than 1 Yahoo email account, please verify with the user if he/she is attempting to log in with the correct (existing in the specific connection) one.
Please let us know your findings! Thank you!
In case more guidance is needed and your subscription covers it, you can submit a support case with specific (sensitive) data so that logs on our side can be verified.