whmcsTools/move_fund_invoice_due_date.php

<?php

// this hook offsets the due date of an invoice for add fund using order grace days

if (!defined("WHMCS"))
    die("This file cannot be accessed directly");

use WHMCS\Database\Capsule;
function get_grace() {
    $grace = Capsule::table('tblconfiguration')->where('setting', 'OrderDaysGrace')->first();
}

add_hook('PreInvoicingGenerateInvoiceItems', 1, function($vars) {
    $grace = get_grace();

    logModuleCall(
        'PreInvoicingGenerateInvoiceItems',
        __FUNCTION__,
        $vars,
        "Debug",
        $grace
    );
    
    return true;
});

?>