You are misunderstanding the question.

The tuple in swaps indicate the position where the swapping takes place. As in

• The first swap moves the ball from 0 to 1

• The second swap moves the ball from 1 to 2

• The final swap doesn't affect the position of the ball. (Because ball is currently at index 2, so the swapping of 0th-indexed and 1st-indexed cup do not affect the ball)

Note that we are only concerned of the final position of the ball and not the validity of each swapping nor the index / position of invalid swaps.

Can someone help me in this kata description example?
(start = 0 ; swaps = [(0, 1), (2, 1), (0, 1)] ) --> 2

Ball from 0 go to 1 then 2,1 is invalid, and 0,1 is also invalid? Then the answer should be 1? I didnt see any move end in 2?

Yes mine failed with price = 54 discount = 5 holiday_cost = 8856