You need to go into PaperUI and expose the new Items to the myopenhab cloud.
Then, these Items will be visible to Alexa also.
Your tag is also wrong:
Instead of: ["lighting"] use [ "Lighting" ] (capital L is mandatory… spaces are optional)
by the way: this item is a “dummy” Item (meaning that it is not bound to anything)… Is this intentional or you want to bind it to a KNX Channel?