Proper to put notes with coin (6)
I believe the answer is:
decent
'proper' is the definition.
(synonyms)
'notes with coin' is the wordplay.
'notes' becomes 'de' (two musical notes).
'with' is a charade indicator (letters next to each other).
'coin' becomes 'cent' (cent is a kind of coin).
'de'+'cent'='DECENT'
'to put' is the link.
(Other definitions for decent that I've seen before include "reasonable" , "Proper; passable" , "Proper and suitable" , "Respectable; satisfactory" , "Polite - fitting" .)