What is the best way to avoid Multi Dex error while installing new plaugins?

Hello, I am totally sick of multi dex problem. At first I got those problem when I installed

1. Google mobile ads
2. Facebook
3. Facebook Audience Network

Then I solved this problem by deleting the common jar files from the facebook audience network >plugins>android> lib.

But after that when I imported the facebook mediation plugin then I got multi dex Error.

Code (CSharp):

1. * What went wrong:
2. Execution failed for task ':transformDexWithDexForRelease'.
3. > com.android.build.api.transform.TransformException: com.android.ide.common.process.ProcessException: java.util.concurrent.ExecutionException: com.android.dex.DexException: Multiple dex files define Lcom/google/android/exoplayer2/source/dash/BuildConfig;

Even importing unity ad mediation also gives me multidex error while building.

Even if I try to build the project only
1. Google mobile ads
2. Facebook
3. Unity Ad Mediation

then I also get the multi dex error.

Not only those plugin If i tried to import onsignal plugin it also gives me multi dex while building.
Please give me a solution for this multi dex problem.