Additional amount (3-2)
'additional amount' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for top-up that I've seen before include "Extra addition" , "Amount required to restore something's level" , "Additional amount to restore mobile phone credit, for example" , "Replenished drink" , "Supplement" .)
'additional amount' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for more that I've seen before include "Greater quantity or number" , "Additional or larger amount" , "victim of Henry" , "What Oliver wanted" , "A greater amount" .)