You can get quick answer of your question by entering here
Why customer is not able to Check-In on the airline website using PNR and Email ID?
We advise Check-In using the PNR and the passenger's last name. Please note that there’s an exception for special fares. If you selected a special fare type during booking, this will be updated in the airline records 24 hours before the departure, and your boarding pass will be emailed by the airline 12 to 6 hours before departure to you or you can check the same on the airline website, it will be updated.