By performing some tests on the message form under the block of the seller I realized that clicking on it and sending messages are sent to the site administrator and not the seller. correct bugs for pleasure.

@fabgan
That will be some issue on your side, maybe with mail sending.
You can check the code:
oc-content/plugins/instant_messenger/user/create_thread.php

Communication is created between sender (logged user) and receiver (owner of listing).
    $from_user_id = (osc_is_web_user_logged_in() ? osc_logged_user_id() : null);
    $from_user_name = ( Params::getParam('im-from-user-name') <> '' ? Params::getParam('im-from-user-name') : osc_logged_user_name() );
    $from_user_email = ( Params::getParam('im-from-user-email') ? Params::getParam('im-from-user-email') : osc_logged_user_email() );


    $to_user_id = $item['fk_i_user_id'];
    $to_user_name = $item['s_contact_name'];
    $to_user_email = $item['s_contact_email'];

Send step by step guide how to reproduce on demo site.