I may have mentioned this before but it's still worth repeating....
Today, I tried to book a mess of airline, train and bus tickets. After multiple tries, they were all declined. I used three different cards with three different banks. Nothing.
I should mention I'm in Lithuania. None of the bookings were in Lithuania. Even after I verified with the banks. So I wondered if my location could have something to do with it?
Perhaps.
I thought I'd try something different. I brought up my VPN and set my connection to the country where I was buying the tickets.
All went though without a glitch.
So, if you're having trouble buying a ticket, get a VPN and connect through the country where you are buying the ticket. It may work.