Believe in a positive balance (6)
I believe the answer is:
credit
I believe this is a double definition.
'believe' is the first definition.
(thesaurus)
'a positive balance' is the second definition.
'in' acts as a link.
(Other definitions for credit that I've seen before include "Belief - trust - favourable acknowledgment" , "Time given to pay for goods" , "Note acknowledging a source of information" , "Good reputation; tick" , "Direct (anag) - tick" .)