Update #2 - 9th June 2021, 17:30 BST
It seems that Nintendo of Europe (as this exploit only seemed to be available briefly in Europe) has closed the loophole so that no-one will get the Hyrule Warriors: Age Of Calamity Expansion Pass for free; that's fair enough, right?
Emails have gone out to customers that downloaded the "purchase bonus" and then had accounts showing that they'd 'purchased' the Expansion Pass. The short summary is that you don't get the expansion content for free, and due to the fix implemented it won't be possible to legitimately buy the content until its launch day, when the system will presumably refresh and the option to purchase will return. The full email is below.
On Friday May 28th 2021, the Hyrule Warriors: Age of Calamity Expansion Pass was made available for purchase on Nintendo eShop. Buying the Expansion Pass entitles users to a special Purchase Bonus of equippable items that can be used in-game immediately.
Unfortunately, an error on Nintendo eShop led to the Purchase Bonus being briefly made available to all users. Furthermore, downloading the Purchase Bonus without buying the Expansion Pass gave the impression that the Expansion Pass was then purchased, when this is not the case. As you are one of the users affected, we'd like to apologise for this error.
Currently, users who downloaded the Purchase Bonus without buying the Expansion Pass are able to equip the related items in-game. However, once Expansion Pass Wave 1 – Pulse of the Ancients becomes available, these items will no longer be usable unless the Expansion Pass is purchased. This will not affect your save file or ability to play the game.
Users affected by this issue are currently unable to purchase the Expansion Pass via Nintendo eShop. This will be resolved once Expansion Pass Wave 1 – Pulse of the Ancients is released, at which point the purchase button will be accessible again.
Once again, we apologise for this error and any inconvenience caused.
Update 28th May 2021, 20:30 BST — Looks like the eShop error has been corrected.
Original Story: Now, we can't guarantee that this deal will be permanent, we can't guarantee that you'll be able to keep it, and we definitely can't guarantee that it'll be the case for long, but right now it looks like you can grab the Hyrule Warriors: Age Of Calamity Expansion Pass for free, thanks to an exploit.
If you download the free "purchase bonus" on the eShop (search for "Hyrule Warriors" and it should be the second result), it looks like you'll get the Expansion Pass too, saving yourself a tidy £17.99 — as confirmed by a few of our staff members. The exploit even works if you don't own the game, so you can bank it for future use, if you want.
We've only confirmed this to work on EU accounts, although some people have discovered that you can grab the Expansion Pass on an EU account and it'll work in-game even if you're playing on a US account, at least.
The purchase bonus was made available today, and includes a new weapon and costume for Link. The Expansion Pass is split into a June and a November release. You can check out what's included in each in the image below.
Let us know if this works for you!