Why is there a decline in my AdSense revenue?
Check the reason behind it.
probable reason may be
-less traffic
-low RPM
-low CTR
-fewer impressions
If you find anything unusual you can write to Google for help.
Hope your earnings will improve soon.
You have placed your ads in the wrong position place as per Google guidelines, make back links, do proper SEO on-page SEO, target keywords everywhere in H1 tag, alt tags content increase traffic at your website, this will improve your Google adsense earning.