Check from your server
Is Rhino online?
Look for Rhino in the member list. If it shows as online, run ,ping. A reply means Rhino is up and the problem is in the server's settings.
Is Rhino still in the server?
When a monthly plan runs out, Rhino posts a notice and leaves. If it's gone from the member list, renew in the support server.
Did the prefix change?
Staff may have changed the server's prefix, or you may have set one of your own with ,selfprefix, which replaces the server's for you. The slash command /help works whatever the prefix is.
Is the command switched off?
Commands and whole modules can be disabled per channel or per member. ,disabledlist shows what's off.
Can Rhino speak in that channel?
Check that the channel doesn't deny Rhino the Send Messages or Embed Links permission.
Is Rhino's role high enough?
Rhino can only act on members and roles below its own role. Drag its role above the ones it manages.
If Rhino is offline
An outage affects every server at once. Check the support server for a notice before changing your settings. Your settings stay as they are while Rhino is down.
Discord itself has outages too. Its own status page is the place to check when every bot in your server goes quiet at once.