If your Effective CPM (eCPM) appears to be lower than your Minimum CPM, it does not mean ads were displayed at a price lower than your Min CPM. Ad rendering, invalid activity filters, and other factors can cause the calculation of eCPM to appear lower than your minimum price threshold.
Learn more about how eCPM is calculated.
Common reasons eCPM might be lower than your Min CPM
Ads not fully rendered
Sometimes a website pre-fetches a rich media ad for later delivery, but that ad is never fully rendered.
Invalid activity filtering
Estimated revenue is adjusted for various correction factors, such as invalid activity filtering, which are not filtered out from the impression numbers used to calculate eCPM.