Crossword Genius

Quickly visit Post Office to get code for debit card (3,2)

Ross

I believe the answer is:

pop in

I'm a little stuck... Click here to teach me more about this clue!

'quickly visit' is the definition.
'pop in' can be an answer for 'visit' (thesaurus). I am not sure about the 'quickly' bit.

'post office to get code for debit card' is the wordplay.
I cannot quite understand how this works, but
'post' could be 'p' (abbreviation as in PS for postscript) and 'p' is found in the answer.
'code' could be 'pin' (a PIN number is a 4-digit code) and 'pin' is present in the answer.
A single letter 'o' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for pop in that I've seen before include "Pay a quick informal visit" , "Visit briefly" , "Call" .)

I've seen this clue in The Guardian.
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