We're updating the way eCPM floors are set up in AdMob.
By setting an eCPM floor, you’re instructing the AdMob Network not to serve ads that are below the minimum eCPM floor value you've set.
Previously, the eCPM floor value was entered when you created a mediation group. Starting today, you should instead set the AdMob Network eCPM floor value when you create or edit an ad unit. The eCPM floor can be set for each of your ad units, individually.