As mentioned in Getting a transit card, almost all transit in the entire country can be paid for by a single transit card (usually a T-Money card). However, for transit from the airport, there are three main exceptions:
While paying for taxis with a transit card is common, they also directly accept foreign credit cards.
As mentioned here, the Airport Express runs two types of trains: all-stop (blue) and express (orange). For the all-stop train, you simply tap a transit card (or purchase a single-use ticket) to enter and ride on any train, the same way as a subway. For the express train, however, you should buy a seperate, timed ticket at the machines, which you can pay by credit card, and no transit card is required (in fact, it's not even possible to pay by transit card).
Ticket Machine for All-Stop Train
(Can Skip if Using Transit Card)
Ticket Machine for Express Train
(Must Use, Can Not Use Transit Card)
To take an airport bus to the airport, no ticket is required and you simply pay by tapping your transit card (the same as any other bus). However, to take an airport bus from the airport, a pre-purchased timed ticket is required, which can be purchased from the airport bus vending machines at the airport.
