Reply to private note to a third party via API

Hello,

I would like to know if there is any way to send note to a third party (contact, external email).

I have tryed this following request but got an error :

{
	"body": "Hello :) ",
	"notify_emails": ["myman.external@foodomain.com"],
	"user_id": 123456789
}

And the error :

{
    "description": "Validation failed",
    "errors": [
        {
            "field": "notify_emails",
            "message": "Accepts only emails of agents",
            "code": "invalid_value"
        }
    ]
}

to the endpoint "https://domain.freshdesk.com/api/v2/tickets/1000000/notes" method "POST".

Why i need to do this ? It's because i would like to respond to a forward's response.

I have forwarded the ticket "1000000" to a non-agent email (so an "external"), that external has responded to the forwarded mail, so in Freshdesk this was translated into an internal note. And finaly i would like to respond to that external using Freshdesk API. But when i'm trying to add note and specify his email adress in notify_emails (see request above) i got the error because he is not an agent.

I hope