I found the solution

<?php if(!osc_is_web_user_logged_in()) {
    osc_add_flash_error_message(__('Please log in to see your conversations.', 'instant_messenger'));
    header('Location:' . osc_user_login_url());
    exit;
   } else { ?>
Thank you very much

Cool, thanks for sharing

It is working properly now
Is writing the code this way correct?
I think the code is a bit long
Can it be shortened?
<?php if(!osc_is_web_user_logged_in()) {
    osc_add_flash_error_message(__('Please log in to see your conversations.', 'instant_messenger'));
    header('Location:' . osc_user_login_url());
    exit;
   } else { ?>
<?php if(osc_is_web_user_logged_in() && $item['fk_i_user_id'] <> osc_logged_user_id() || !osc_is_web_user_logged_in()) { ?>Thank you all

@7ala
Code looks to be correct.