Common Issues

Members can't open tickets

"You already have an active ticket" — each member can have one open ticket at a time. Close it, or point them to the channel the message names.
"Blacklisted" — check /blacklist list.
Ticket creation fails — the bot likely lacks Manage Channels on the category. See Discord Permissions.

You need Administrator or an Elevated Role. Staff without one should use /closerequest.

Message	Fix
"Only admins can reopen a ticket by number"	You need Administrator or an Elevated Role.
"not found"	Check the number against the closure log — it's the part after the last dash.
"is not closed"	The ticket is still open, claimed, or waiting on a scheduled close.
"already has an active ticket"	The opener has another open ticket. Close it first.
"category … no longer exists"	Re-create the category or set its Discord location, then retry.
"opener is no longer in this server"	The member has to rejoin first.

Check which of these applies:

The ticket is claimed. Claiming hides it from support roles. Roles that should always see it go in 👁️ See-All Roles.
The category has its own support roles. Those replace the global ones for that category. Add the role to the category, or to 👁️ See-All Roles.
The role only has Elevated. Elevated Roles can close instantly but can't see tickets. Also add a support or see-all role.
The ticket was open before you changed support roles. Support role changes only affect new tickets (See-All Roles update open tickets right away).

The opener has DMs closed, or DM Transcripts is disabled. The log channel copy is always available if a log channel is set.

A prerequisite is off — for example Edit Agreement needs Agreement enabled, and Set Plugin List needs Source Select.