Proof that someone has settled (7)

I believe the answer is:

receipt

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'proof' is the definition.
(I have seen 'Proof of purchase' mean 'receipt' so perhaps 'proof' could also mean 'receipt')

I can't explain the rest of the clue.

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(Other definitions for receipt that I've seen before include "Sales slip" , "Proof of purchase" , "A written acknowledgement; a word used in the first ever 2 dn" , "Perhaps slip" , "Formally acknowledge" .)

I've seen this clue in The Globe and Mail.

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