<div class="ttfmake-overlay-happyforms-ad">
    <?php $url = add_query_arg( array(
        'tab' => 'plugin-information',
        'plugin' => 'happyforms&happyforms=1',
        'TB_iframe' => true,
    ), network_admin_url( 'plugin-install.php' ) );

    _e( sprintf( '<b>Need a contact form?</b> <a href="%s" class="thickbox open-plugin-details-modal">Install HappyForms for free</a>, it\'s specially designed to work with Make theme.', $url ), 'happyforms' ); ?>
</div>