function closePendingInvoice($invoiceObj)
 {
     $invoiceId = $invoiceObj->id;
     $subscriptionId = $invoiceObj->subscriptionId;
     $startDate = $invoiceObj->startDate;
     $endDate = $invoiceObj->endDate;
     $chargeInCents = MeterBilling::getUsageCharge($startDate, $endDate, $subscriptionId);
     $addChargeParam = array("amount" => $chargeInCents, "description" => "monthly usage");
     /*
      * Calling ChargeBee Add Charge Invoice API and add Charge to invoice 
      * based on the usage made by customer.
      */
     ChargeBee_Invoice::addCharge($invoiceId, $addChargeParam);
     $addonQuantity = MeterBilling::getQuantityUsed($startDate, $endDate, $subscriptionId);
     $addAddonCharge = array("addonId" => "wallpapers", "addonQuantity" => $addonQuantity);
     /* 
      * Calling the ChargeBee Add Addon Charge Invoice API and add the no of 
      * addons used by customers to the invoice.
      */
     ChargeBee_Invoice::addAddonCharge($invoiceId, $addAddonCharge);
     /*
      * Closing the invoice and Collecting the payment(if auto collection is on)
      * by calling the ChargeBee Collect Invoice API.
      */
     ChargeBee_Invoice::collect($invoiceId);
 }