function my_popup_logic( $can_access, $user_id, $popup_id ) {

    if ( $popup_id == 1234 && ! wpf_has_tag( 'Tag Name' ) ) {
        $can_access = true;
    }

    return $can_access;

}

add_filter( 'wpf_user_can_access', 'my_popup_logic', 10, 3 );