Being in harmony in Reggae mix (8)
I believe the answer is:
agreeing
'being in harmony' is the definition.
(I've seen this before)
'in reggae mix' is the wordplay.
'mix' indicates anagramming the letters.
'in'+'reggae'='inreggae'
'inreggae' with letters rearranged gives 'AGREEING'.
(Other definitions for agreeing that I've seen before include "achieving harmony" , "OK" , "At one" , "In accord" , "Correspondent" .)