Fish to be paid for at the door? (3)

I believe the answer is:

cod

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'fish' is the definition.
(type of fish)

I don't understand the remainder of the clue.

(Other definitions for cod that I've seen before include "Not a real" , "Initially, pay when you get the goods" , "A fish; a hoax (slang)" , "to be paid for when it arrives" , "Pull the leg of - a fish?" .)

I've seen this clue in The Independent.

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