There are a couple common reasons why you might see this.
- You've displayed a CPM ad for which an advertiser paid less than 1 cent. Advertisers may pay as little as $0.50 for each 1000 impressions of an ad. With each impression worth $0.0005, you could receive up to 9 ad impressions for total revenue of $0.0045.
- You may have received some clicks that our monitoring system deemed invalid. As you may know, we monitor all clicks on Google ads for any activity that may artificially drive up an advertiser's costs or a publisher's earnings. Clicks that our system considers invalid will still appear in your reports. However, because our advertisers aren't charged for these clicks, we won't show the earnings for this activity. Learn more about invalid clicks.
Rest assured that AdSense accounts are properly credited for all clicks and impressions we consider to be valid. Finalized earnings will be included in your Payments page at the end of every month.