The !glownotify command sometimes yields an informative error/documentation message, but not in all cases; on at least one occasion it produced a different, less informative error message. I haven't figured out exactly what the criteria are. Places where it would be nice to produce it include:

• !help glownotify
• !glownotify invalidsyntax
• !glownotify in a channel with insufficient permissions (additional error-message information here would be helpful)
• !glownotify in DM

For reference, the message:

swag !glownotify: Manage subscriptions for glowfic post Minimum Arguments (2): [subscribe|unsubscribe] [URL of post|Author name]

("swag" is underlined; I don't know of a way to produce that in sourcehut markdown.)