The main purpose of order_reference parameter is to match the payment in EveryPay’s system to the correct corresponding order in merchant’s e-shop. By default, the order_reference value is required to be unique. As an additional benefit, matching the order_reference and validating its uniqueness in merchant’s e-shop provides an extra layer of security against tampering attacks. However, if needed the order_reference uniqueness validation can be turned off. When disabled, multiple payment attempts are allowed for one order reference until a successful payment is performed.