Ignite - otherwise it's free! (3,4)

I believe the answer is:

set fire

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'ignite' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'otherwise it's free' is the wordplay.
'otherwise' indicates anagramming the letters.
'its'+'free'='itsfree'
'itsfree' anagrammed gives 'SET FIRE'.

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

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