Ad size and an unit id must be set before ad load

Ad size and an unit id must be set before ad load
I’m facing this error anyone please help

Also my impression rate decreasing dag by day

You have set eCPM high ($0.50) and Google is not displaying video ads at this time due to which the impressions are low and earnings getting so low.

First I’m not using video ads
Second I’m using optimize cpm

Good to know