chatwoot api - create message

Question

I would like to send a message with the chatwoot api. https://www.chatwoot.com/developers/api/#tag/Messages/operation/create-a-new-message-in-a-conversation

I tried this code:

<?php

    
    $ch = curl_init("https://mydomain.de/api/v1/accounts/1/conversations/100/messages");
    curl_setopt($ch, CURLOPT_POST, TRUE);
    curl_setopt($ch, CURLOPT_HEADER, FALSE);
    curl_setopt($ch, CURLOPT_MAXREDIRS, 10);
    curl_setopt($ch, CURLOPT_TIMEOUT, 30);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, TRUE);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
    curl_setopt($ch, CURLOPT_FRESH_CONNECT, TRUE);
    curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
    curl_setopt($ch, CURLOPT_ENCODING, '');
    curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query(
        array(
                "content"       =>  "string",
                "message_type"  =>  "outgoing",
                "private"       =>  true,
                "content_type"  =>  "cards"
        )
    ));
    curl_setopt($ch, CURLOPT_HTTPHEADER, 
        array (
            'api_access_token: XXX'
        ),
    );


    $response = json_decode(curl_exec($ch), true);
    curl_close($ch);
    
    
    echo '<pre>';
    print_r($response);
    echo '</pre>';


?>

Response:

Array
(
    [errors] => Array
        (
            [0] => You must log in or register before you can proceed.
        )

)

Any idea?