Hi,
The PayPal Express checkout plugin we developed already add the shipping fee to the setExpressCheckout API call provided that your cart already has the shipping fee added to it.
I looked at your website checkout, and I can see that the shipping fee is only added after the customer has entered his address on your checkout. So you should display the PayPal Express button on your checkout only after that.
Normally, to do that, you want to have the "cart" view in a step after the step where you have login/address views in your HikaShop Checkout workflow. However, from what I see on your checkout, you have all the views in the same step which lead to the people being able to express checkout before HikaShop is able to add the shipping to the cart.
Now if you want to allow customers to express checkout before they enter their address on your checkout, it requires the implementation of the PayPal Instant Update / Callback API to send the shipping rules to PayPal so that they can be charged dynamically by PayPal:
stackoverflow.com/questions/8647278/payp...shipping-calculation
However, the structure accepted for the shipping rules won't allow for a generic solution and is complex to implement. So most payment plugins (for Hikashop or other ecommerce solutions) don't implement it and it's done as a custom development if necessary.
Note that if you want to allow People to pay with PayPal while only allowing them to access the PayPal payment after the shipping fees are added, while not changing your checkout structure, I would recommend to go with the PayPal standard payment method instead of the Express checkout. That's because the goal of the Express checkout API of PayPal is precisely to skip the checkout on your website, but in your case, you apparently don't want to skip the checkout on your website since you need your checkout to calculate the shipping fees. In that case, PayPal standard is more adapted.