Shopify Add to Cart Error Fix

I hope you can help me. I am working on a wholesale shopify site for a client. They want the ability to add multiple product variants to the basket. I have found some code that creates the matrix but when I add numbers to the matrix and click Add the products do not transfer to the cart.

You can see the product page here:

https://tri-distribution.myshopify.com/collections/frontpage/products/rwc-2019-mens-l-s-basic-rugby-shirt

and I found the original code here:

https://community.shopify.com/c/Shopify-Design/add-to-cart-multiple-variants-quantities/m-p/129555

Does this sound like something you would be able to solve for me? If so please let me know and I will give you any further details you require.

Thanks in advance,

Ian