Posting a message requires a user to be logged in. You then submit to the support/messages/new-message form action to post the message.
The following is an example of posting a new message:
<form method="post" accept-charset="UTF-8">
{{ csrfInput() }}
<input type="hidden" name="action" value="support/messages/new-message">
<input type="hidden" name="ticketId" value="{{ ticket.id|hash }}">
<textarea name="message" placeholder="Post a message"></textarea>
<input type="submit" value="Post message">
</form>Note that both the ticketId and message fields are required.
The ticketId field must contain a valid ticket ID that is hashed to prevent tampering.