Crossword Genius

That little extra that makes the star higher (3-2)

Ross

I believe the answer is:

top-up

I'm a little stuck... Click here to teach me more about this clue!

'that little extra that' is the definition.
I can't tell whether this defines the answer.

'the star higher' is the wordplay.
I cannot really see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
'higher' could be 'up' and 'up' is present in the answer.
The remaining letters 'op' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

'makes' acts as a link.

Can you help me to learn more?

(Other definitions for top-up that I've seen before include "Supplement" , "Amount required to restore something's level" , "Additional amount to restore mobile phone credit, for example" , "Extra addition" , "Replenished drink" .)

I've seen this clue in the Evening Standard.
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