Slip covering bottom, reportedly (7)
I believe the answer is:
receipt
'slip' is the definition.
(slip of paper acting as a record of a purchase)
I cannot understand how the remainder of the clue works.
(Other definitions for receipt that I've seen before include "old cook's directions" , "Proof of payment made" , "Record of payment" , "Written or printed acknowledgement or payment" , "Sales slip" .)