message: billing - minor - better log
diff: @@ -267,6 +267,7 @@ export default abstract class BillingIntegration {
  tenantID: this.tenant.id,
  source: Constants.CENTRAL_SERVER,
  action: ServerAction.BILLING_TRANSACTION,
  + actionOnUser: billingInvoice.user,
  module: MODULE_NAME, method: 'sendInvoiceNotification',
  message: `Failed to send notification for invoice '${billingInvoice.id}'`,
  detailedMessages: { error: error.stack }
  