After generating some Admob impressions with Appodeal, you will notice a lot of requests for your app in Admob dashboard with low match rate. Don't worry, it happens, because Admob counts requests for each ad unit.
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This is how it works: 

When you sync your Admob account, the Appodeal plugin creates multiple ad units on your behalf and sets different price floors for each ad unit. Ad units with higher price floors tend to produce lower fill rate. However, each ad format has ad units without price floors and their performance should always be close to 100%. Check Appodeal dashboard for the actual fill rate as we count requests to each specific network.

If you have issues with Admob fill rate, please read this article.