Compared across countries

What do you do if the ticket gate won't open?

For a trip that crosses borders — the same question, answered country by country.

The pattern

Both treat an underpaid fare as a machine's job rather than an argument. The adjustment machine sits inside the gates, and you settle there before you leave.

Japan

Use the fare adjustment machine inside the gates to top up in cash, or take it to the staffed gate beside them.
South Korea

Top up at a fare adjustment machine near the turnstiles. It handles both a T-money card and a single journey ticket.

Sort the practical stuff before you fly.