The most common and most likely answer to this crossword clue is the 2 plus 1 plus 6 letter word BE A PLAYER
B
E
A
P
L
A
Y
E
R
Buddy explains!
The straight part
We know that "Have an important interest in" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case have an important interest in = be a player.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.