Was obliged to pay nothing, you and I, on the day (4)
I believe the answer is:
owed
'was obliged to pay' is the definition.
(I've seen this before)
'nothing you and i on the day' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'you and i' becomes 'we'.
'on' is a charade indicator (letters next to each other).
'the day' becomes 'd' (abbreviation for day).
'o'+'we'+'d'='OWED'
(Other definitions for owed that I've seen before include "to be paid" , "Had a duty to pay" , "Outstanding" , "Was obliged to pay" , "Was due to pay" .)