There's nothing we have to repay (3)
I believe the answer is:
owe
'have to repay' is the definition.
(I've seen this in another clue)
'there's nothing we' is the wordplay.
'there's nothing' becomes 'o' (I've seen this in other clues).
'o'+'we'='OWE'
(Other definitions for owe that I've seen before include "Bear" , "Have to thank" , "Are debtors" , "Need to pay" , "overdrawn" .)