At liberty to make no charge (4)
I believe the answer is:
free
I believe this clue is a double definition.
'at liberty' is the first definition.
('free' can be similar in meaning to 'at liberty')
'no charge' is the second definition.
('free' can be a synonym of 'gratis')
'to make' acts as a link.
(Other definitions for free that I've seen before include "Not under restraint" , "unoccupied)" , "Reef (anag.)" , "without payment" , "with no toll demanded?" .)