The getavatarsseats command will return all avatars and primitive UUIDs representing objects that the avatar is sitting on as a CSV list.

llInstantMessage(CORRADE,
    wasKeyValueEncode(
        [
            "command", "getavatarsseats",
            "group", wasURLEscape(GROUP),
            "password", wasURLEscape(PASSWORD),
            "callback", wasURLEscape(URL)
        ]
    )
);

The command will return a primitive UUID if successful or will fail with an error otherwise.

• The command is the singular form of batchgetavatarseat.
• This command is radar-bound.