If you are trying to scan Welcome Amiibo cards that say "Not supported" on the bottom, double-check you have installed the v1.5 update. The base game ignores them. Once patched, your European 3DS becomes the ultimate portable Animal Crossing machine.
Version 1.5 update Animal Crossing: New Leaf – Welcome amiibo Animal Crossing- New Leaf Update v1.5 3DS -EUR ...