Sun Express Airlines Forced Me to Pay Extra €5 by Not Allowing Online Check-In

I just booked a flight with Sun Express and had a problem with their online check-in process. I filled in all my info right, but the system just wouldn’t let me finish the check-in. I had to check in at the airport, and they hit me with an extra €5. Looks like this isn't just a one-off problem. I've come across a bunch of other people saying the same thing about Sun Express not letting them check in online, probably just to hit them with that fee at the airport. I think this practice is unfair and makes things inconvenient for customers like me. I hope Sun Express can sort this issue out and make their online check-in system better, so passengers don’t end up getting charged or facing any hassle.