Why is my balance negative?:SI
Your Diamonds balance may turn negative if you have spent the Diamonds for your recent purchase in the game and then reversed the payment shortly afterwards.
Such actions will result in your account balance turning into a Negative balance.
You may want to refill the balance by purchasing Diamonds in order to cover the difference in balance that has appeared.
Also, you can wait for the required amount of Diamonds to accumulate naturally by conducting Missions and completing achievements.