add_action('wpf_woocommerce_payment_complete', 'my_wpf_woo_complete', 10, 2);

function my_wpf_woo_complete( $order_id, $contact_id ) {

    $payment_method = get_post_meta( $order_id, '_payment_method', true );
    if($payment_method == 'cheque') {
        wp_fusion()->crm->apply_tags(array(123), $contact_id);
    }

}