Help needed in cash register challenge

I do not know what to do in this challenge .
please explain me , I am stuck.
the confusion part for me is the third argument (cid).

cid stands for “cash in drawer”, it says how much cash is available for each denomination - you need to use it to determinate if the change can be given or not and how much of each denomination to give

for example : ["TWENTY", 60]
that means 60 bills of twenty dollars (1200 $) or 60 dollars in total (3 bills of 20 dollars);

it’s the total value, 60$

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Thank you very much for your help