please consider upgrading to the packman distribution of the unity ads SDK. Asset Store distribution will not longer be supported after unity 2018.3

Problem : please consider upgrading to the packman distribution of the unity ads SDK. Asset Store distribution will not longer be supported after unity 2018.3

Solution :

it means that you should install Unity ads SDK from the package manager,
by going to window -> Package Manager and
then selecting Advertisement package.

Option 1 :

option 2 :

option 1 : SDK version is 3.0.0

option 2 : SDK Version is 3.4.2

GO TO Option 2.