Reply to sort pie out (7)
I believe the answer is:
riposte
'reply' is the definition.
(riposte is a kind of reply)
'sort pie out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'sort'+'pie'='sortpie'
'sortpie' anagrammed gives 'RIPOSTE'.
'to' acts as a link.
(Other definitions for riposte that I've seen before include "Quick answer" , "Repartee; quick thrust (fencing)" , "Snappy comeback" , "Poster I alter for repartee" , "Rejoin" .)