confused about a question in the kaplan exam kit for fia

carter purchased goods from miller which were found to be faulty.
what is the double entry in carter’s accounting record to account for the return of those goods ?
a. debit:purchase returns Credit:accounts payable
b. Debit :accounts payable and Credit:purchase returns

in my head i worked it out as debit account payable as carter doesnt owe that money anymore and account payable in a liability account and decrease in liability is a debit entry.
and credit purchase returns account .
so that b
but according to the book its a.
i know its very basic but i dont know what am i missing here .
any help would be appreciated
thanks