Substitutes put up with error (6,2)
I believe the answer is:
stands in
'substitutes' is the definition.
('stand in' can be a synonym of 'substitute')
'put up with error' is the wordplay.
'put up with' becomes 'stand' ('stand' can be a synonym of 'put up with').
'error' becomes 'sin' (I've seen this in other clues).
'stand'+'sin'='STANDS IN'
(Other definitions for stands in that I've seen before include "Acts as sub" , "deputy" , "acts for the moment" , "Deputises" , "Substitutes" .)