Hi Nicolas,
OK, I have been trying to get this to work for a few days. I created a category called "Shipping Fees" in the root of the store, and made sure the category was not published. Then I created a product called "Additional Crate Fee", made sure it was published and assigned it to the "Shipping Fees" category. I placed your code in the location you noted, and made sure that the XX's were changed to the ID number of the "Additional Shipping Fee" product.
I have a few sample products in the store now, each with different weights. When I add products from the store that do not add up to 150lbs, and click the "Proceed to checkout" button in the mini-cart, it takes me to the checkout page without problems.
If I add products to the cart that add up to over 150lbs, and click on the "Proceed to checkout" button, the page just keeps going through a continuous and quick regenerating cycle between two pages. It appears that one page is blank, while the other page shows what looks like a partial, unformatted view of the checkout page. It displays simple boxes for billing address, shipping address, payment information, and coupon code. When I stop the page from continuously regenerating, it is blank, but the URL shows one of the two following ......com/online-store/product/updatecart/product_id-4/quantity-1/add-1/return-aHR0cDovL3d3dy5kaXlraXRjaGVuYW5kYmF0aC5jb20vb25saW5lLXN0b3JlL2NoZWNrb3V0 -or- .....com/component/hikashop/checkout
When I press the back button in the web browser, it returns to the website home page. At the beginning of the page it shows and error of "No shipping method found", except that it is displayed over 20 times. Maybe from the continuous regenerating? I want to note that I do not have my shipping methods defined yet. Additionally, in the mini-cart, it shows the "Additional Crate Fee" product added in the cart. I changed the "Maximum quantity per order" option for the "Additional Crate Fee" product, otherwise it would show a large quantity in the mini-cart after pressing the back button, and I only want to have it added one time. So it appears that maybe some of the code is working because the "Additional Crate Fee" has been added, but it is obviously not working the way it should. All this is in Google Chrome.
Do you have any ideas why this is not working, and what I can do next to get it working. I feel that we are close, and I can get this working with just a little fixing.
Thank You,
Chris