Visa-free transit and the arrival card
Two separate rules that people constantly merge into one. Getting them confused is how a short connection becomes a long conversation.
Visa-free transit and the arrival card are different things with different conditions. The first depends on your nationality, your route and your onward ticket. The second is a form most arrivals fill in.
Transit: the route matters more than the passport
Transit policies require a confirmed onward ticket to a third country or region — not back to where you came from. That single condition disqualifies more travellers than any other.
The arrival card
There is an official mobile form, it is free, and it can be completed before you land. Anyone charging for it is not official.