To send a message to a contact, provide the contact’s email address in the
to_contact field. To send a message to a channel, provide the channel’s ID in
Rate Limit Label:
The message to be sent.
The email address of the contact to whom you would like to send the message.
The Channel Id of the channel where you would like to send a message.
Chat mentions object. Use this object to include mentions in the message that will be sent to a channel.
Message ID: Unique Identifier of the message.