Send message to a lead

The ID of the lead to send a message to.

The content of the message to send to the lead.

The date and time to schedule the message for. This should be in ISO 8601 format (e.g. 2024-05-17T21:09:13Z). If not provided, or if the scheduled time is in the past, the message will be sent immediately.

Whether to send the message even if Apten is turned off for the lead. Defaults to false.

Returns "Message sent successfully." if the message was sent.