Maybe make marks with key on daughter’s lucky purchase? (11)

I believe the answer is:

scratchcard

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But I can't explain it at all! Could you help me understand?

(Other definitions for scratchcard that I've seen before include "Gambler's investment rubbed with a coin" , "form of lottery" , "Ticket for instant lottery" , "Rubbed lottery ticket" .)

I've seen this clue in The Times.

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