Let me add that I was able to book tickets online using my desktop computer (iMac, Safari). No issues, passport number was needed for me and partner, credit card was no issue getting it through, just needed to confirm with the card company (this was a couple weeks ago and I do not remember what it asked for other than it was no issue to comply.) Tickets were emailed, and also something texted to my phone which I think is both a receipt and the ticket/seat.
I do not use apps on my phone, I am old school with my desktop, or iPad when I am traveling, and have yet to have an issue.