The order number/reference refers to the whole order which includes the customer's details, payment/delivery method and the status of the order.
Some orders may have more than one voucher which is why individual voucher numbers/codes are also needed.
When a customer comes in or calls up to use their voucher you need to ask for their unique voucher code so you can then redeem the voucher on your dashboard. Once redeemed it will show in the order details that this voucher has now been used. The image below shows two example voucher codes.
It should be the customer purchasing the vouchers who would know the order reference and then only the recipient who would only know the voucher codes (for any vouchers that have been sent). In some cases, the customer may call up to change the details or check the status of their order and this is when you’d need the order reference.