Turkish Airlines Online Check-in Issue for Zanzibar Holiday Package

We purchased a Zanzibar holiday package with Turkish Airlines Holidays. Despite having a Business class return ticket, I was able to check-in online while my friend received a warning that they needed to check-in at the airport counter before the flight. We called the call center, but they couldn't assist either. We drove 1.5 hours to the airport. The website states that the TK office at the airport operates from 09:00 to 17:00. We arrived at 13:00, but it was closed with no one inside. My concern is that I saw all seats were occupied during my online check-in. Maybe that's why my friend couldn't check-in. We paid for Business class tickets and faced these issues. If there's no seat available, TK, be prepared because I will be very upset. I hope to see the day when TK faces consequences for these repeated issues!