Game activated and downloaded with game code... not playable

My kids have a Nintendo Switch 1 and have their own account that isn’t linked to the Nintendo eShop. I created my own account so that I could activate a game using its activation code. I added my account to the Switch, entered the activation code for the game Shinobi, which was downloaded and activated as I can see its icon on the console’s home screen. When I click on it, it takes me to the eShop and asks me to buy it or to download the demo version. I don’t want to buy it again as I’ve already entered the activation code. So I can’t play it. What did I do wrong or what should I do.