Charge, briefly, involves money invested on top of everything else (2,3,2,3)
I believe the answer is:
to cap it all
'on top of everything else' is the definition.
(I've seen this before)
'charge briefly involves money invested' is the wordplay.
I cannot really see how this works, but
'money' could be 'capital' (I've seen this before) and 'capital' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for to cap it all that I've seen before include "On top of everything else" , "the worst of the lot" , "as a last straw" , "Finally" , "To provide the finishing touch" .)