Mark Customer/Vendor Invoice/Invoices for settlement using X++ in D365 or AX 2012

Below method can be used to mark the Invoice amounts for settlement in very easy way.

In your code to loop through ledgerjournaltrans(assuming you already created payment lines for respective Customer/vendor, if not, then create payment record either by X++ or direct entry through payment screens).

Just for reference, i am creating payment via x++ and marked the invoices for settlement.
I am posting full process (create & Post SO, Create Payment entry, Mark invoice for settlement, post payment entry)

form class Declaration.

public class FormRun extends ObjectRun
{   
    CustTable   custtable_g;
    CustInvoiceJour     bitcustInvoiceJour;
}

Below method can be used for SO creation and Payment entry.

public void TestReceipt()
{
    SalesTable salesTable;
    NumberSeq NumberSeq;
    SalesLine salesLine;
    SalesFormLetter formLetterObj;
    InventTable inventTable;

    Ledgerjournalname           ledgerjournalname;
    LedgerjournalTable          LedgerjournalTable;
    LedgerjournalTrans          LedgerjournalTrans;
    LedgerJournalCheckPost      ledgerJournalCheckPost;

    ;

    try
    {
        ttsBegin;
        //Create sales header
        NumberSeq = NumberSeq::newGetNumFromId(SalesParameters::numRefSalesId().NumberSequenceId);
        salesTable.SalesId = NumberSeq.num();
        salesTable.initValue();
        salesTable.CustAccount = custtable_g.AccountNum; //custtable_g is already initialized
        salesTable.initFromCustTable();
        salesTable.insert();

        //Create Sales lines
        salesLine.clear();
        salesLine.SalesId   = salesTable.SalesId;
        salesLine.ItemId    = ItemId.valueStr(); 
        inventTable = InventTable::find(ItemId.valueStr());
        salesLine.initFromInventTable(inventTable);
        salesLine.SalesQty  = Quantity.value();
        salesLine.createLine(NoYes::Yes, // Validate
        NoYes::Yes, // initFromSalesTable
        NoYes::Yes, // initFromInventTable
        NoYes::Yes, // calcInventQty
        NoYes::Yes, // searchMarkup
        NoYes::Yes); // searchPrice

        //confirmation
        //formLetterObj = SalesFormLetter::construct(DocumentStatus::Confirmation);
        //formLetterObj.update(salesTable,Selldate.dateValue());

        //Packing Slip
        formLetterObj = SalesFormLetter::construct(DocumentStatus::PackingSlip);
        formLetterObj.update(salesTable,Selldate.dateValue());

        //Post Invoice
        formLetterObj = SalesFormLetter::construct(DocumentStatus::Invoice);
        formLetterObj.update(salesTable,Selldate.dateValue());

        ttsCommit; 

        //
        ttsBegin;
        bitcustInvoiceJour = formLetterObj.parmJournalRecord();

        //Generate and post receipt

        select ledgerjournalname where ledgerjournalname.JournalName == "PayJ"; //use correct payment journal name

        //ttsBegin;
        LedgerjournalTable.JournalName = ledgerjournalname.JournalName;
        LedgerjournalTable.initFromLedgerJournalName();
        LedgerjournalTable.JournalNum  = JournalTableData::newTable(LedgerjournalTable).nextJournalId();      
        LedgerjournalTable.insert();

        numberSeq                               =   NumberSeq::newGetVoucherFromId((ledgerjournalname.NumberSequenceTable));
        LedgerjournalTrans.Voucher              =   numberSeq.voucher();
        LedgerjournalTrans.JournalNum           =   LedgerjournalTable.JournalNum;
        LedgerjournalTrans.AccountType          =   LedgerJournalACType::Cust;
        LedgerjournalTrans.Company              =   curext();
        LedgerjournalTrans.parmAccount(custtable_g.AccountNum,LedgerjournalTrans.AccountType);
        LedgerjournalTrans.initFromCustTable(custtable_g);
        LedgerjournalTrans.TransDate            = Selldate.dateValue();

        LedgerjournalTrans.ExchRate             =   Currency::exchRate(LedgerjournalTrans.CurrencyCode);

        LedgerjournalTrans.Txt                  =   strFmt('Payment for item sale for sales id : %1',salestable.SalesId);


        LedgerjournalTrans.DefaultDimension         =   custtable_g.DefaultDimension;
        LedgerjournalTrans.OffsetDefaultDimension   =   custtable_g.DefaultDimension;
        LedgerjournalTrans.TransactionType          =   LedgerTransType::Payment;
        LedgerjournalTrans.AmountCurCredit          =   bitcustInvoiceJour.InvoiceAmount;
        LedgerjournalTrans.PaymMode                 =   CustPaymMode.valueStr();
        LedgerjournalTrans.SettleVoucher            =   SettlementType::SelectedTransact;
        LedgerjournalTrans.modifiedField(fieldNum(LedgerjournalTrans,PaymMode));
        LedgerjournalTrans.insert();


        element.settlement(LedgerjournalTrans,LedgerjournalTrans.AmountCurCredit); //look for method

        //Post Journal
        ledgerJournalCheckPost = LedgerJournalCheckPost::newLedgerJournalTable(LedgerjournalTable,NoYes::Yes);
        ledgerJournalCheckPost.run();

        ttsCommit;
      
        info(strFmt("Journal %1 created for item sales Id %2 to Student id %3",LedgerjournalTable.JournalNum,salestable.SalesId,custtable_g.AccountNum));

    }
    catch
    {
        error("error in generating receipt for sale.");
    }


}

Below method can be used for settlement of required amount

void settlement(ledgerJournalTrans _ledgerJournalTrans,real _amounttoSettle)
{
    SpecTrans insertSpecTrans;
    ;
    insertSpecTrans.SpecCompany = _ledgerJournalTrans.Company;
    insertSpecTrans.SpecTableId = TableNum(ledgerJournalTrans);
    insertSpecTrans.SpecRecId   = _ledgerJournalTrans.RecId;
    insertSpecTrans.RefCompany  = _ledgerJournalTrans.Company;
    insertSpecTrans.RefTableId  = TableNum(custTransOPen);
    insertSpecTrans.RefRecId    = custTransOPen::findRefId(bitcustInvoiceJour.custTrans().RecId).RecId;
    insertSpecTrans.Balance01   = _amounttoSettle;
    insertSpecTrans.Code        = _ledgerJournalTrans.CurrencyCode;
    insertSpecTrans.Payment     = NoYes::No;
    insertSpecTrans.LineNum     = 1;
    insertSpecTrans.insert();

}

yes, I am done here. Thanks!!!