Happy over credit increase (6)

I believe the answer is:

uptick

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'increase' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'happy over credit' is the wordplay.
'happy' becomes 'up' (I've seen this in other clues).
'over' means one lot of letters go next to another (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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