[hermanzegerman]

It's mandatory by law, and it's additionally to the 3 numbers at the back of the card. Usually it works by confirming or denying the transaction on the App of your Issuing bank

[beAbU]

None of the eu amazons have 2fa on their card transactions.

[hermanzegerman]

Why do they say otherwise on their own website?

https://www.amazon.de/b?ie=UTF8&node=17666138031

[beAbU]

Well I have bo idea. All I know is when I purchase on either .de, .co.uk or .ie the transaction goes through immediately. I have 3D secure enabled.

The text on that link of yours is sneaky though:

"...you MAY be asked to..." (Emphasis mine)

[hermanzegerman]

Because you can add them to a "That Store is safe" list, and you won't get asked again. You probably did this at some point

[antonkochubey]

They recently enabled 3DS for business accounts, on customer ones it’s indeed still disabled