Package used in tutorial https://www.youtube.com/playlist?list=PLUtXDWVV2ZDqNZd1Fm4Jks9wocXqj-Fpp

#Admob Mediation - Show unity ads and admob ads together

https://www.youtube.com/playlist?list=PLUtXDWVV2ZDrzw2UCAbVP6xhLxhuptDgm

In recent version's play service resolver is replaced with External Dependency resolver. If you want to update the admob or firebase to recent version.

Do these things

1 - Delete Play Service resolver folder

2 - Delete file related to admob in folder Asset -> Plugin -> Android.

3 - Import the new package with external Dependency resolver