Nintendo has implemented some pretty stringent anti-piracy measures for the Switch, and according to one console hacker, it has already started banning game cart certificates. In a lengthy PSA on the SwitchHacks subreddit, "SciresM" said Nintendo can now quickly detect if the game you're trying to play online has been legitimately purchased, whether it's a game cart or a digital copy. The gaming giant performs server-side checks, so you can't bypass them -- if it determines that you're playing a legit copy, it issues an authorization token that can't be forged. In case it catches you trying to play a pirated copy, it will prevent your game from connecting and could even permanently ban your console from being able to access the Nintendo network.
Looks like we've got confirmation that Nintendo is banning gamecart certificates (I guess people aren't taking my advice...). The relevant error for trying to use a gamecard with a banned cert is 0x1F727C -- 2124-4025.— Michael (@SciresM) June 20, 2018
These strict anti-piracy measures come after the rise of hacks on the Switch following the discovery of an exploit that allowed hackers to run arbitrary code on the console. While it's easy to dismiss them if you don't actively play pirated games, you may still want to keep them in mind if you buy second-hand game carts. Try to check if the copy works and isn't already banned before playing it on your console if you can, so as not to risk getting locked out of online play.