No online purchasing with gift voucher

I got a gift voucher in April 2021. Now that I finally see something worth buying online, I am not able to. Apparently, according to Longile from customer service, a gift voucher can no longer be used online. And when I asked her since when she says that it has been a long time. She was so rude and impatient and clearly not even attempting to be helpful. This is very confusing as the payment options online gives the option for gift voucher and on the back of the gift voucher card it gives instructions how to purchase online with it. Why is the website not updated? Why is the gift vouchers issued still claiming you can use it online? So am stuck with this worthless gift voucher. Business is online and I cannot understand what the reasoning can be behind refusing your own gift cards online.