The Listening Party chat is open to all logged-in fans by default. You’ll have the option to turn on Supporter-only Chat to limit the chat to fans who have purchased something from you, or leave it open to everyone with a fan account. You can turn Supporter-only Chat on or off at any time using the Listening Party Editor or the Chat Settings panel.
Since Listening Parties are free, some attendees may not qualify as supporters. Toggling on the Supporter-only Chat can limit the number of people engaging in the chat, and its main purpose is to prevent less serious (or in the rare and worst case, bad-acting) attendees from entering the chat conversation.