PAYMENT_SOURCE_CANNOT_BE_USED and mismatch of amounts in the request

Hi!

Using “Paypal upon invoice” always shows the error PAYMENT_SOURCE_CANNOT_BE_USED.
We discussed some different approaches with the Paypal Merchant Technical Support, but the configuration itself was OK.

They found the following problem in the logs of our requests:
“Notice that there is a mismatch between amounts, i.e., sum of item amount are not matching the transaction amount. Hence, the error is prompted. The total amount in purchase_unit is : 13.50 but the total in items add up to only 8.40.”

"purchase_units": [
        {
            "amount": {
                "breakdown": {
                    "item_total": {
                        "currency_code": "EUR",
                        "value": "8.40"
                    },
                    "shipping": {
                        "currency_code": "EUR",
                        "value": "2.94"
                    },
                    "tax_total": {
                        "currency_code": "EUR",
                        "value": "2.16"
                    }
                },
                "currency_code": "EUR",
                "value": "13.50"
            },
            "custom_id": "XXXX",
            "description": "",
            "invoice_id": "XXXX",
            "items": [
                {
                    "category": "PHYSICAL_GOODS",
                    "description": "XXXX",
                    "name": "XXXX",
                    "quantity": 1,
                    "sku": "XXXX",
                    "tax": {
                        "currency_code": "EUR",
                        "value": "0.00"
                    },
                    "tax_rate": "0.00",
                    "unit_amount": {
                        "currency_code": "EUR",
                        "value": "8.40"
                    }
                }
            ],

The missing amount are taxes and shipping costs, which is, according to the Paypal technical support, the reason for the error message for “Paypal upon invoice”.

As far as I can see, it is not possible for me as an admin to change the way the API call is done to Paypal. The Technical Support also says, that this is on behalf of the plugin author.

How can this be resolved?

Thanks,
Marc