If you still play Splatoon for the Wii U, then you should know that the SplatNet service for the game will end on September 30th. However, as expected, the online multiplayer will still be available.
“The SplatNet service for the Splatoon game on the Wii U system will be permanently closed on September 30th, 2017. Online multiplayer battles will still be available, as this update only affects the SplatNet service. We sincerely thank all players for using this companion site for the original Splatoon game.”