Firebird's fee? Nothing they say! (7)
I believe the answer is:
phoenix
'firebird's' is the definition.
(I've seen this before)
'fee? nothing they say' is the wordplay.
I cannot quite see how this works, but
'nothing' could be 'nix' (nix can mean nothing) and 'nix' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for phoenix that I've seen before include "Legendary bird -- Arizona city" , "Arizona city (that rose from the ashes?)" , "capital in America" , "Firebird" , "Fabled bird" .)