You are unable to join an online match, and you receive the error code 2618-0542.
If you receive this error, it indicates the room you are attempting to join has reached the maximum amount of players.
If you receive this error when attempting to join a friend's match, then this indicates the room that friend is in has reached the maximum amount of players.
What to Do:
Wait a while and try to join the match again a little later.
If you would like further assistance with the Nintendo Switch console, please contact Nintendo Customer Service.