QBO IPP API - how to link a payment to an invoice

Question

I am able to successfully create an invoice, and a payment, but don't seem to be able to properly link the payment to the invoice. I have tried several variations, but it either does not link at all, or I get a "Business Validation Error: Unexpected Internal Error." error in my error logs. Below is my c# code. Is there a simplified way (example) of linking a payment to an invoice?

Invoice i = QBGet_InvoiceByMDVInvoiceNum(MDVInvoiceNum);
Payment p = new Payment();
Customer customer = QBGet_CustomerByName(ClientName, "CompanyName");
Account acc = QBGet_AccountsReceivableAccount();

p.TxnDate = DateTime.Now;
p.TxnDateSpecified = true;
List<Line> lineList1 = new List<Line>();
Line pmtLine = new Line();
pmtLine.Amount = ReceivedPaymentAmt;
pmtLine.AmountSpecified = true;
List<LinkedTxn> linkedTxnList = new List<LinkedTxn>();
LinkedTxn linkedtxn = new LinkedTxn();
linkedtxn.TxnId = i.Id;
linkedtxn.TxnType = "invoice";
linkedTxnList.Add(linkedtxn);

pmtLine.LinkedTxn = linkedTxnList.ToArray();

//p.LinkedTxn = linkedTxnList.ToArray();

lineList1.Add(pmtLine);
p.Line = lineList1.ToArray();

p.CustomerRef = new ReferenceType()
{
    Value = customer.Id
};

p.DepositToAccountRef = new ReferenceType() { Value = acc.Id };
p.PaymentRefNum = ReceiptCheckNo; 

p.TotalAmt = ReceivedPaymentAmt;
p.TotalAmtSpecified = true;

DataService service = new DataService(context);
var result = service.Add<Payment>(p);

I have also tried this approach:

p.CustomerRef = new ReferenceType()
{
    Value = customer.Id
};
p.PrivateNote ="ReferralID: " + ReferralId + "\r\n" + "PaymentDetailID: " + PaymentDetailID + "\r\n" + Comments;
p.PaymentRefNum = ReceiptCheckNo;
p.PaymentType = PaymentTypeEnum.Check;
p.PaymentTypeSpecified = true;
p.DocNumber = MDVInvoiceNum;
p.TotalAmt = ReceivedPaymentAmt;
p.TotalAmtSpecified = true;
p.TxnDate = PaymentReceivedDate;
p.TxnDateSpecified = true;

LinkedTxn[] lt = {new LinkedTxn()
{
        TxnId=i.Id,
        TxnType="invoice"
    }
};

Line l = new Line()
{
    Amount = ReceivedPaymentAmt,
    LinkedTxn = lt
};

Line[] aryL = {l};
DataService service = new DataService(context);
Payment pmt = service.Add(p);

p.Line = aryL;
p.LinkedTxn = lt;

Payment pmt2 = service.Update(p);

Answer 1

Sharing the Java code and corresponding working JSON payload. It might help.

private void paymentAgainstInvoice() {
    Payment payment = new Payment();
    Date currentDateTime = null;
    try {
        currentDateTime = DateUtils.getCurrentDateTime();
    } catch (ParseException e) {
        e.printStackTrace();
    }
    payment.setTxnDate(currentDateTime);

    Line line = new Line();
    line.setAmount(new BigDecimal("100"));
    LinkedTxn linkedTxn = new LinkedTxn();
    linkedTxn.setTxnId("248");
    linkedTxn.setTxnType("Invoice");
    List<LinkedTxn> linkedTxnList = new ArrayList<LinkedTxn>();
    linkedTxnList.add(linkedTxn);
    line.setLinkedTxn(linkedTxnList);
    List<Line> lineList = new ArrayList<Line>();
    lineList.add(line);

    payment.setLine(lineList);

    ReferenceType custReferenceType = new ReferenceType();
    custReferenceType.setValue("29");
    custReferenceType.setName("ABC");
    payment.setCustomerRef(custReferenceType);

    payment.setTotalAmt(new BigDecimal("100"));
    ReferenceType accountRefType = new ReferenceType();
    accountRefType.setValue("63");
    payment.setPaymentRefNum("ABC-100-Invoice");
    payment.setDepositToAccountRef(accountRefType );

    try {
        this.service.add(payment);
    } catch (FMSException e) {
        e.printStackTrace();
    }
}

JSON payload ( Payment )

{
   "CustomerRef":{
      "value":"29",
      "name":"ABC"
   },
   "DepositToAccountRef":{
      "value":"63"
   },
   "PaymentRefNum":"ABC-100-Invoice",
   "TotalAmt":100,
   "TxnDate":"2014-11-30",
   "Line":[
      {
         "Amount":100,
         "LinkedTxn":[
            {
               "TxnId":"248",
               "TxnType":"Invoice"
            }
         ]
      }
   ]
}