Should I enter Authentication Code if I am trying to clear validation details for the first time during a day?

No. While trying to clear validation details for first time, you will not have the Authentication Code, hence you are not required to enter this value. You can proceed by entering other details for validation on this screen (i.e., Receipt Number and statement summary details). On completion of validation, Authentication Code will be generated and displayed when you proceed to next page. You may copy the code and keep for re-using it during the same day..