Owing to bad pun, help is needed (6)
I believe the answer is:
unpaid
'owing' is the definition.
(similar in meaning)
'bad pun help is needed' is the wordplay.
'bad' is an anagram indicator.
'help' becomes 'aid' (synonyms).
'is needed' says to put letters next to each other.
'pun' with letters rearranged gives 'unp'.
'unp'+'aid'='UNPAID'
'to' acts as a link.
(Other definitions for unpaid that I've seen before include "Overdue" , "Outstanding, owing" , "Not give wages" , "Honorary" , "Without reward" .)