D365 Finance and operation

 public  void settlePayments(CustTable _custTable)
    {
        CustTrans  payCustTrans;
        CustTrans custTrans;
        CustTransOpen custTransOpen, custTransPayment;

        SpecTransManager specTransManager;
        boolean doSpecTransRecordsExist = false;
        Amount  sumInvAmountCur; 
        boolean     markedInvoices;

        // create a specification offset voucher for the current customer
        SpecTransExecutionContext specTransExecutionContext = SpecTransExecutionContext::newFromSource(_custTable);
        specTransManager = SpecTransManager::newFromSpec(specTransExecutionContext.parmSpecContext());
// Serach for latest payment for selected customer
  while select custTransPayment
            order by TransDate asc
            where custTransPayment.AccountNum == _custTable.AccountNum
            && custTransPayment.AmountMST < 0
             join payCustTrans
            where payCustTrans.RecId == custTransPayment.refrecId
            && payCustTrans.TransType == LedgerTransType::Payment
            //&& !payCustTrans.LastSettleDate
        {
            amount += abs(custTransPayment.AmountMST);

            if (!specTransManager.exist(custTransPayment.DataAreaId, custTransPayment.TableId, custTransPayment.RecId))
            {
                doSpecTransRecordsExist = true;
                custTrans = custTrans::find(custTransPayment.RefRecId);
                specTransManager.insert(custTransPayment.DataAreaId,
                                            custTransPayment.TableId,
                                            custTransPayment.RecId,
                                            custTransPayment.AmountCur,
                                            custTrans.CurrencyCode);
            }
        }

        // Clear the table buffers.
        custTransOpen = null;
        custTrans = null;
        custInvoiceJour = null;

        // add open invoice transactions to the offset voucher
        while select custTransOpen
                order by TransDate,RecId asc
                where custTransOpen.AccountNum == _custTable.AccountNum
                && custTransOpen.AmountMST > 0
                && custTransOpen.AmountMST <= amount
                join CurrencyCode from custTrans
                where custTransOpen.RefRecId == custTrans.RecId
        {
            if(custTransOpen.AmountCur <= amount)
            {
                amount -= custTransOpen.AmountCur; 
            }
            else
            {
                continue; 
            }
            doSpecTransRecordsExist = true;
            markedInvoices = true; 
            sumInvAmountCur += custTransOpen.AmountCur;
            // check to see if the record already exists in the specManager before
            // adding it again - this will help from having over settlement issues.
            if (!specTransManager.exist(custTransOpen.DataAreaId, custTransOpen.TableId, custTransOpen.RecId))
            {
                doSpecTransRecordsExist = true;
                
                specTransManager.insert(custTransOpen.DataAreaId,
                                        custTransOpen.TableId,
                                        custTransOpen.RecId,
                                        custTransOpen.AmountCur,
                                        custTrans.CurrencyCode);
            }
        }

        // settle the transactions
        if(markedInvoices)
        {
            CustTrans::settleTransaction(specTransExecutionContext, CustTransSettleTransactionParameters::construct());
        }
        else if (doSpecTransRecordsExist)
        {
            specTransManager.deleteAll();
        }