Alliance Academy Boost Error ‘Investment Error - Not enough Boosts’;

This generally happens when there is a difference between the game value and backend value of the number of boosts. 

Restarting the game should sync the values and the error should go away. 

Don't worry, the boost did not apply, the Cash also did not get deducted from your account.

Restarting the game will bring the cash back, in-case it got deducted.