Credit involves primate in scheme (5)
I believe the answer is:
caper
'scheme' is the definition.
(I have seen 'illegal scheme' mean 'caper' so perhaps 'scheme' could also mean 'caper')
'credit involves primate' is the wordplay.
'credit' becomes 'cr' (abbreviation).
'involves' is an insertion indicator.
'primate' becomes 'ape' (large primate).
'cr' enclosing 'ape' is 'CAPER'.
'in' acts as a link.
(Other definitions for caper that I've seen before include "Dance; pickled bud" , "Pickled bud - escapade" , "Skip about for the sauce" , "Skip or dance around" , "that may be cut by the energetic?" .)