Troubleshooting

Symptom	Cause	Fix
/sd says unknown command for players	Command blocked by CommandWhitelist, or the player lacks showdown.command.menu	Whitelist showdown, sd and ranked. Test as a non-op
Player cannot join a queue	Team breaks the format, or they are in a tournament or match	The join message names the rule that failed
Queue never starts a match	No enabled arena with the pvp tag on this server	Check /sd arena
Ranked win paid nothing	Repeat-opponent heat, fewer than the minimum turns, a draw, or the match ended on events and the player has not been back to main yet	Expected. Check ranked_reward_matches for the reason
Draft players not moved to events	[server] names wrong, or the events server is down	Check both servers' [server] sections. Turn on debug.tournamentStatusLogging
A ranked battle is frozen	Pixelmon battle stuck	/sd match save <player>, end it, then /sd match restore <player>

Boot lines that show it loaded correctly:

Showdown commands registered.
Showdown: registered <n> permission nodes.
Showdown ready. Rulesets: <n>, Arenas: <n>, Economy: lazy (checked on first use)