Well I'll go to Japan soon, by Turkish airlines and my boyfriend that's in Japan bought the ticket for me by expedia. I know that some airline companies can ask to show the credit card and if that happens I'll be in trouble. So I thought about do the check in online, but I'd like to know if that will prevent the problem. I'll go from Portugal and do a layover of 2 hours in Turkey, it's a round trip and I'll not need have to do check in again in turkey because the air company is the same, so I'll just stay in the transit area. Another question is what I can do to prove that my boyfriend agreed in paying me the ticket. I can bring with me a digital copy of his credit card, Id card and a declaration how he accepted pay the ticket with his signature and handwriting?
Airlines tickets are always issued to a specific person that's named on the ticket. Only that person can travel on this ticket, regardless of who paid for it. So as long as your name is on the ticket (and the booking) you are fine.
I do buy tickets for my kids that live in different countries all the time. All they need at the airport is the confirmation number (or booking reference) and a valid ID that matches the passenger name on the booking.