Why does AlphaCommerceHub respond `1059` / «Internal Processing Error please resend the request» to a PayPal's `RefundPayment` API request?

Extensions AlphaCommerceHub
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1

The PayPal’s RefundPayment API request is documented in the Where is the request and response parameters specification for the PayPal’s RefundPayment transaction? article.
But it does not work for me.

1. Request

1.1. Body

{
    "Header": {
        "MerchantID": "ANTERIOR001",
        "TransactionType": "RefundPayment",
        "UserID": "<...>",
        "Version": "2"
    },
    "Transaction": {
        "Amount": "169000",
        "Currency": "AUD",
        "MerchantTxnID": "1208L.773",
        "Method": "PP"
    }
}

1.2. Headers

Request: POST / HTTP/1.1
Accept-encoding: gzip, deflate
Connection: close
Content-Length: 298
Content-Type: application/json
Host: hubapiuat.alphacommercehub.com.au
User-Agent: Mage2.PRO

2. Response

{
    "Banks": null,
    "Country": null,
    "DocumentResults": null,
    "EmailChecks": null,
    "FraudChecks": null,
    "GeoChecks": null,
    "Result": {
        "Amount": "169000",
        "Currency": "AUD",
        "custom1": null,
        "custom2": null,
        "custom3": null,
        "custom4": null,
        "custom5": null,
        "MerchantID": "ANTERIOR001",
        "MerchantTxnID": "1208L.773",
        "ResponseCode": "1059",
        "ResponseMessage": "Internal Processing Error please resend the request",
        "ResponseTimestamp": "11122017090314"
    },
    "ShippingService": null,
    "TaxResultLines": null
}
2

If to resend the same request again (as AlphaCommerceHub recommends: «please resend the request»), then the response is 10009 / «Transaction refused. The partial refund amount must be less than or equal to the remaining amount.»

{
    "Banks": null,
    "Country": null,
    "DocumentResults": null,
    "EmailChecks": null,
    "FraudChecks": null,
    "GeoChecks": null,
    "ProviderResps": {
        "ProviderResp": [
            {
                "ProviderName": "Paypal",
                "ProviderOrder": "1",
                "ProviderResponse": "10009",
                "ProviderResponseMessage": "Transaction refused. The partial refund amount must be less than or equal to the remaining amount."
            }
        ]
    },
    "Result": {
        "custom1": null,
        "custom2": null,
        "custom3": null,
        "custom4": null,
        "custom5": null,
        "MerchantID": "ANTERIOR001",
        "MerchantTxnID": "1208L.773",
        "ResponseCode": "1015",
        "ResponseMessage": "Transaction not allowed",
        "ResponseTimestamp": "11122017090911"
    },
    "ShippingService": null,
    "TaxResultLines": null
}
3

I have got a response from AlphaCommerceHub:

Can you check again.
There was a host file error on one node meaning you were probably receiving this randomly.
That was corrected yesterday.

4

The next errors: