I was looking to purchase a license for a xenforo forum, when I saw that there was a 1 year extension deal for just an extra $40. I read the details, but I don't see a place where I would be able to apply that extension for a total of $180 on my purchase.
The first 12 months of support are included in the purchase price.
Once the license has been purchased, you can purchase the extension should you wish to do so.
For reference, $40 is not a special deal, that is the standard price.