Ryanair ... just recently I went with my 3 kids with them. I did a mistake in paying an adult ticket for my oldest son instead of teenager ticket. This small mistake made it impossible to do the checkin online. It was impossible to correct this mistake online, they referred to customer support which I was not able to reach at all despite many attempts. So I decided to do the checkin at the airport instead. After waiting around 30 minutes in the line I explained them why I was not able to do the checkin online. They then spent 25 MINUTES trying to solve the mistake, she had to make 3 phone calls and get help from her manager to try to change the ticket from adult to teenager. Of course I had to pay €30 per person for doing the checkin at the counter instead of online. I made it in time but the line at the checkin grew a lot as everyone was waiting to solve the issue. So stupid.