Pay back rum, beer is free (9)
I believe the answer is:
reimburse
'pay back' is the definition.
(I've seen this before)
'rum beer is free' is the wordplay.
'free' indicates an anagram.
'rum'+'beer'+'is'='rumbeeris'
'rumbeeris' is an anagram of 'REIMBURSE'.
(Other definitions for reimburse that I've seen before include "Repay a person who has spent or lost money" , "refund" , "Repay (a sum of money)" , "Financially compensate" , "Pay back any expenses incurred" .)