Happy over credit increase (6)

I believe the answer is:

uptick

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'increase' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'happy over credit' is the wordplay.
'happy' becomes 'up' (I've seen this in other clues).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'credit' becomes 'tick' (on tick can mean purchased on credit).
'up'+'tick'='UPTICK'

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