How can I add extra charges for non-serviceable pincodes at checkout?

[adorna]

Hi,

I have an issue where certain pincodes are being charged extra as they are non-serviceable and this incurs additional charges apart from the Shipping charge that is displayed at checkout. What happens is that, we are notified of the extra charge only during the time of dispatch and this makes us go back and forth to the customer to collect the amount before dispatch. I have the list of such pincodes with me but cannot seem to input it in Shopify.

To avoid this I was thinking, if Shopify can add an additional layer of charge at checkout if the pincode entered by customer is non-serviceable. For example, for such a pincode the checkout page should display PRODUCT TOTAL+SHIPPING FEE+EXTRA CHARGES instead of PRODUCT TOTAL+SHIPPING FEE.

Can this be done within Shopify itself or are there any free apps for this?