Duplicate purchase discussed later (3-3)

I believe the answer is:

bye-bye

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'later' is the definition.
(I've seen this before)

'duplicate purchase discussed' is the wordplay.
'duplicate' becomes 'bye' (I can't explain this - if you can you should give a lot more credence to this answer).
'purchase' becomes 'buy' (buy is a kind of purchase).
'discussed' indicates a 'sounds like' (homophone) clue.
'buy' sounds like 'bye'.
'bye'+'bye'='BYE-BYE'

Can you help me to learn more?

(Other definitions for bye-bye that I've seen before include "Cheerio" , "Childish farewell" , "See you" , "Adieu" , "Informal repetitive farewell" .)

I've seen this clue in the Sydney Morning Herald.

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