You must have version 1.1.7 installed to access online matchmaking.
While this is a minor update, it carries several technical implications for your save data and online play: Dairantou Smash Brothers- DLC Update 1.1.7 3D...
The developers have announced that this is not the end of the DLC updates for Dairantou Smash Brothers. More content, including new characters, stages, and game modes, is planned for future updates. You must have version 1
While "3D" often refers to the version of the game, some players may confuse older version numbers with Super Smash Bros. Ultimate on Nintendo Switch, which has a different update history: including new characters