Can you please check the status of your Experience Service? Whether it is active or turned-off..
Just an FYI, you can find the Experience Service URL under Studio Project Configuration -> Info Tab -> Experience Service field. Copy the URL, append the url which should like "https://<replace-with-url-in-ExperienceService-field>:2019/ExperienceService" or "https://<replace-with-url-in-ExperienceService-field>/ExperienceService". If it is active, it should prompt for User/password, validate with your credentials.