(1) Voucher has to be redeemed (used) on the Iberia airline website. (2) The bonus can be used one or more times, until its amount is exhausted. (3) You will be able to use it whenever you want until Thursday, December 1, 2022.
Please note that the ticketing has to be done via Iberia airlines website only. The actual airline could be Iberia airline or a partner airline - for example United Airlines or British Airways.
While booking the flight, on the payments page, please locate: "Do you have voucher, discount code or gift card" towards the top right corner of the page. Click the check box, and paste the code that you will get from me electronically (email or sparefare). It will zero out the fare that you have selected (if less than $3812) and will show you any balance that you may have left on your voucher.