For a customer to receive event notifications when their unbilled usage balances reach, go above, or go below specified threshold percentages, you must configure the Unbilled Usage Threshold Adjustment Percentage setting.
For example, if you set the unbilled usage balance threshold for various customers to $100 and you want them to receive event notifications when 80% of that threshold is reached, then they receive event notifications when their unbilled usage balance reaches, goes above, or goes below $80.