Coupons to make free products

Hi, I created a coupon to make a free product, my store is only for digital goods and the paying method is PayPal Express. When someone in my store tries to buy that good with the coupon, which makes the download free, they can't buy it because PayPal won't let a purchase for $0 dollars, so how can I make my buyers to download that file for free with the coupon?
Thank you for your help.

add the following code:

<?

if ($WA_Store_Cart->GrandTotal() == 0)  {

  $GLOBALS['WAGLOBAL_Gateway'] = 0;    

}

?>

To the top of the pages:
webassist/plugins/shopping_cart/cart_editable.php
webassist/plugins/shopping_cart/checkout_form.php
webassist/plugins/shopping_cart/cart_readonly.php
webassist/plugins/shopping_cart/process_transaction.php

(note: the code needs to be placed immediately below the ->GetContent() call for the cart.)

Thank you Jason, it worked but is there a way when I introduce the coupon code in the cart that another button instead of the PayPal will appear? because I have to give a click to the paypal button and then my purchase is rejected and then when I press go back to checkout the option to buy without PayPal will appear, so that could confuse the costumer.
Thank you for your help

the code edit i suggested should alreaddy be doing that. make sure you have added the suggested code on all 4 of the suggested pages.

Hi Jason, I introduced the code in the pages as you told me.

I'll need to troubleshoot directly, see the private message section.

I test in my Remote Server and local one and still have the same issue.

see private message

I´m sending additional info

Prívate message