Add fee if product variant is in cart

Question

I am trying add fee(+50) to order if user have in cart specific product with specific variant ID. In cart and checkout page should also display custom text. This is my current code:

add_action( 'woocommerce_cart_calculate_fees', 'shipping_weight_discount', 30, 1 );
function shipping_weight_discount( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;
    $percentage    = 0;
    $product_id = 1761;
    $variation_id = 1853;
    $cart_id = WC()->cart->generate_cart_id( $product_id, $variation_id);
    if( WC()->cart->find_product_in_cart( $cart_id ) ) {
    $percentage = 50;
}
    

    if( $percentage > 0 ) {
        $discount = $percentage;
        $cart->add_fee( sprintf( __( 'Množstevní sleva %s', 'woocommerce' ), $percentage.'%'), +$discount );
    }
}

seems $percentage is 0 and it is reason, why is not fee apllied

Answer 1

Please try below code:

add_action( 'woocommerce_cart_calculate_fees', 'shipping_weight_discount', 30, 1 );
function shipping_weight_discount( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;
    $percentage    = 0;
    $product_id = Your_product_id;
    $variation_id = Your_variation_id;
  if( in_array( $product_id, array_column( WC()->cart->get_cart(), 'product_id' ) ) && in_array( $variation_id, array_column( WC()->cart->get_cart(), 'variation_id' ) ) ) {
    $percentage = 50;
}
    

    if( $percentage > 0 ) {
        $discount = $percentage;
        $cart->add_fee( sprintf( __( 'Množstevní sleva %s', 'woocommerce' ), $percentage.'%'), +$discount );
    }
}

It is tested and working good.

Please don't forget to update the product id AND variation id in the above code

Please let me know if you find any issues.