A list of unicode strings representing the reactions you want to remove from this message. Removing a reaction that does not exist will have no effect and will not return an error. An error is returned if a reaction is both added and deleted in the same request.
The attachments you want to remove from this message. Removing an attachment that doesn't exist has no effect and won't return an error. Attempting to add and remove the same attachment in one request is an error.
The URL of the icon to show next to the message. This is only used for action_message messages; other messages show the avatar of the author. If an action_message does not have an icon set, no icon is shown.
The type of message this is. A user_message is a message that the author sent. An action_message is a message about something that happened, such as the thread being resolved. The default value is user_message.