Use on Iberia.com and use voucher code at checkout process.
"The Gift Card can be used once or as many times as you want until you've spent the full amount.
You can use it whenever you want until: 01/08/23
Valid for any direct flight or any connecting flight where at least one of the routes is operated by Iberia Regional Air Nostrum,Iberia Express,Iberia
To fly whenever you want until 01/08/23"