Difficulty for the first currency (7)
I believe the answer is:
trouble
'difficulty' is the definition.
(trouble can mean a difficult situation)
'the first currency' is the wordplay.
'the first' becomes 't' (1st letter of 'the').
'currency' becomes 'rouble' (Russian rouble).
't'+'rouble'='TROUBLE'
'for' acts as a link.
(Other definitions for trouble that I've seen before include "Difficulty, problems" , "Discord" , "Cause distress to; unrest" , "Conflict" , "Disquiet" .)