Unity banner ads very low eCPM

Hello there,

I have 2 problems:
:one: Why is my banner ad eCPM so low while my interstitial ad eCPM is normal?
:two: Not only that, when testing ads on production, only the interstitial ad is displayed, but the banner ad gets the error: NO_FILL - Placement receives no fill.

Please help me,
Thank you.