Flutter taken up? There’s an amount to pay (3)
I believe the answer is:
tab
'an amount to pay' is the definition.
'flutter taken up?' is the wordplay.
'flutter' becomes 'bat' (as in to bat one's eyelids).
'taken up?' says the letters should be written in reverse.
'bat' back-to-front is 'TAB'.
'there's' is the link.
(Other definitions for tab that I've seen before include "Running bar bill" , "Small flap - bill" , "Flap; illicit drug pill (slang)" , "Flap; meal bill" , "Marker" .)