I add this lines on rep107.php
Line: 142
$custrecord = get_customer_details($branch['debtor_no']);
$creditBalance = $custrecord["Balance"];
and then on line: 199
$rep->Font('bold');
$rep->TextCol(3, 6, _("TOTAL INVOICE"), - 2);
$rep->TextCol(6, 7, $DisplayTotal, -2);
line: 199
$rep->NewLine();
$creditBalance = number_format2($creditBalance,$dec);
$rep->TextCol(3, 6, _("Total Debit / Credit"), -2);
$rep->TextCol(6, 7, $creditBalance, -2);