diff --git a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/MenuHelper.h b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/MenuHelper.h
index 6f6a1df..dafd9ad 100644
--- a/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/MenuHelper.h
+++ b/Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/views/MenuHelper.h
@@ -1489,7 +1489,7 @@ inline bool verifyAllPaymentsCompleted(Controller& m_controller)
     {
         throw std::runtime_error("No authenticated user found.");
     }
-    std::string authenticatedUserId = authenticatedUser->getId();
+    const std::string& authenticatedUserId = authenticatedUser->getId();
     util::Map<std::string, const Invoice*> listOfInvoices = m_controller.getAllInvoices();
     for (int invoiceIndex = 0; invoiceIndex < listOfInvoices.getSize(); ++invoiceIndex)
     {
@@ -1498,7 +1498,7 @@ inline bool verifyAllPaymentsCompleted(Controller& m_controller)
         {
             continue;
         }
-        std::string customerId = invoice->getBooking()->getCustomerId();
+        const std::string& customerId = invoice->getBooking()->getCustomerId();
         if (customerId == authenticatedUserId)
         {
             if (invoice->getStatus() != util::PaymentStatus::COMPLETED)