Adsense earnings showing -40$ "Invalid Traffic - AdSense for Content"

I just remembered when I had a higher deduction once I checked everything in Analytics (linked to adsense) and in the end figured out that I deleted one or two articles and the amount almost exactly matched the deduction.
IIRC: This can happen when the adsense bot checks your page and can't find the page or the code on a page anymore thus can't validate the legitimacy of the earnings.