It could be that your account has some clicks or impressions which google monitoring system considers to be invalid. As you may know, in order to protect the interests of google publishers as well as those of google advertisers, Google monitors clicks on Google ads to prevent any abuse of the AdSense program. Google's proprietary technology analyzes all ad clicks for any invalid click activity that is intended to artificially drive up an advertiser's clicks or a publisher's earnings. Clicks deemed by google monitoring system to be invalid will appear in your reports.
However, since advertisers aren't charged for clicks deemed to be invalid, publishers don't receive any revenue for these clicks. For this reason, you may occasionally notice clicks with no associated revenue. Rest assured that your account is being properly credited for all clicks google consider to be valid.
However, since advertisers aren't charged for clicks deemed to be invalid, publishers don't receive any revenue for these clicks. For this reason, you may occasionally notice clicks with no associated revenue. Rest assured that your account is being properly credited for all clicks google consider to be valid.