Two years ago on our trip to the Netherlands all we did was tap in/out on our credit for the trains, trams, etc. So easy!
(Important to note we arrived via France, then via Belgium on a train not through the airport).
We arrived two days ago at Schipohl Airport for a stopover. We checked in to the airport Sheraton (great choice) then wanted to spend late afternoon/evening in Leiden, which is about 10/15 mins ride (and was the first stop after the airport). The tracks are below the airport. We took the escalator downstairs and our train was there and ready to leave the station. We jumped on...low and behold no tap in/tap out. Ugh, now what? Too late to get off.
The train conductor came by and we explained our situation and apologized. We asked if we could pay him directly. He said yes, but that it would include a fine. And then he said he really didn't want to do that. He also said this was a very common problem with visitors as you actually have to buy train tickets departing from Schiphol upstairs in the airport public access area, not down below where the trains are. Very easy to miss. And there aren't a ton of ticket kiosks. (We looked after our return. And they aren't hidden but they don't stand out.) He had us quickly download the NS app (official Netherlands train app) and helped us buy round trip tickets. We never could have gotten out of the Leiden train station because you have to scan your ticket to get out.
It all ended well, but it was very confusing. We definitely monopolized his time for the entire route and he was nothing but friendly and kind.