There was few known issues is going on, please refer the link.
Power BI users using invalid credentials for refresh operation may see a message saying "The last refresh attempt failed because of an internal service error. This is usually a transient issue. If you try again later and still see this message, contact support. ". Please verify credentials are correct before retrying. Engineers are working to update the error classification and expect it to be deployed by end-of-day 02/25/2020.