I am trying to add a surcharge to anyone who pay with PayPal. There are couples of extensions but the free one don't work too well. Then I was pointed to a direction to put "Negative Discount" under "Shopping Cart Price Rules" to mimic a surcharge.

First I was told to remove the limitation to insert negative amount into discount which now it works. However in the checkout process it doesn't get through PayPal.

Everything works well, it display "Negative Discount" in the shopping cart. The sub-total got updated however the value doesn't seem to pass to PayPal correctly. Upon checking out and choosing PayPal as an payment option it returns with:

PayPal gateway has rejected request. The totals of the cart item amounts do not match order amounts (#10413: Transaction refused because of an invalid argument. See additional error messages for details).

However, if I turn this "Negative Discount" price rule to a positive discount (that actually deduce the sub-total), everything will work perfectly well. So kind of pinpointed the issue to be on having "Negative Discount" to have confused PayPal on receiving a correct sub-total or line-item. I imagine PayPal wouldn't take a positive amount as a "Discount" line-item.

Questions are:

  1. Is there a way to keep using this "Negative Discount" at all? By adding events on modules perhaps?
  2. Is there another way to add surcharge to all orders that paid with PayPal?

Thanks in advance!

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