Over 250 Impressions 0 revenue ?

My application was earning 8 - 10 USD with 70 - 80 video impressions,i started advertising my app on Facebook ,
on 18,19 March over 500 impressions and 0 revenue,
I need an explanation to understand this ad system

No one knows, sometime you gain 2$ dollars for a few dozen impressions, sometimes you gain nothing for thousands of impressions.

You get money for clicks, not impressions.

Can you please write in to us at unityads-support@unity3d.com? If you provide your game ID we can look into any issues or concerns that you have in regards to revenue.

Revenue is generated based on a combination of views, clicks, and installs. There’s no “one unified way” of pre-calculating the revenue.