Group must accept it's wrong - send rude message ... (4)
I believe the answer is:
sext
'message' is the definition.
(I have seen 'Explicit message' mean 'sext' so perhaps 'message' could also mean 'sext')
'group must accept it's wrong' is the wordplay.
'group' becomes 'set' (both can mean a collection).
'must accept' indicates putting letters inside.
'it's wrong' becomes 'x' (X is used to mark something as incorrect).
'set' going around 'x' is 'SEXT'.
'send rude' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sext that I've seen before include "service" , "Explicit message" .)