Furnish empty extension, requiring payment now (5)
I believe the answer is:
endue
'furnish' is the definition.
(I've seen this before)
'empty extension requiring payment now' is the wordplay.
'empty' suggests removing the centre.
'requiring payment now' becomes 'due' (I can't explain this - if you can you should give a lot more credence to this answer).
'extension' with its centre removed is 'en'.
'en'+'due'='ENDUE'
Can you help me to learn more?
(Other definitions for endue that I've seen before include "Supply (with a quality/ability)" , "Invest - supply" , "Provide or imbue" , "Endow (with a quality)" , "Invest (something) with a quality or ability" .)