Billing adress and check in

I have a few questions before I check in for my flight:
On my confirmation details page, it states that I am not able to check in online and I can do it at the airport free of charge. But, because this is my first time booking a flight, why was my passport number not required when I booked the flight? Also, because I booked the flight for both my friend and I using my credit card, will she have any issues when she checks in?
Best Answer
Because you are flying internationally, you have to check in at the airport because the ticketing agent needs to check your passport and make sure that you have all the applicable visas. As for your billing address question, there shouldn't be any issue. People buy airline tickets for groups all the time.
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