PayPal IPN setup: "ship to" ZIP code and auto calculation of shipping charges

I have successfully set up PayPal IPN on my site and it’s working fine. From my PayPal account I have set options to asses shippin开发者_C百科g and tax calculations (only if it’s Iowa). But the only issue is, on the PayPal checkout page it’s asking me to enter the “ship to” ZIP code manually. If I enter and update it, only then is the net payable updated with the shipping and tax charges.

Is there any variable which I could use to send the “ship to” ZIP code which will work directly on the cart and make it auto calculate the charges and show it? I have tried both zip and address_zip variables. Neither of them worked.

By the way, I have multiple items in my cart so I am using the “cart” transaction type.

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You can let Paypal handle the shipping charges itself. Just login to your account and set the zipcode and shipping charges from there :-)