Quick payment method for sea life (3)

I believe the answer is:

cod

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'quick payment method' is the definition.
'cod' can be an answer for 'method' (I have seen 'method of payment' mean 'cod' so perhaps 'method' could also mean 'cod'). I am not sure about the 'quick payment' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for cod that I've seen before include "Pull the leg of - a fish?" , "Cash on delivery, in short, for this fish" , "Fish noted for liver oil" , "Hoax (sl.); fish" , "swimmer" .)

I've seen this clue in The Mirror.

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