Fail to get armies mobilised around capital in Haiti (7)
I believe the answer is:
mishear
'fail to get' is the definition.
(I didn't quite get that)
'armies mobilised around capital in haiti' is the wordplay.
'mobilised' indicates an anagram (I've seen this in other clues).
'around' indicates putting letters inside.
'capital in' suggests taking the first letters.
The initial letter of 'haiti' is 'h'.
'armies' is an anagram of 'misear'.
'misear' enclosing 'h' is 'MISHEAR'.
(Other definitions for mishear that I've seen before include "Get wrong message" , "Pick up wrong" , "Sense (words) wrongly" , "Wrongly catch" , "Incorrectly pick up" .)