flutter with admob mediation adcolony still at 0% fill even after many requests

Question

I'm using admob_flutter: https://pub.dev/packages/admob_flutter And it's working fine on my app until the infamous "Limited Ad Serving" been placed for over 2 months.

Now I decided to add AdColony as mediation. Followed what's written https://developers.google.com/admob/android/mediation/adcolony And still not sure why I still got 0% fill rate.

I'm suspicious that the SDK integration is wrong. Last time when I wrote this on my app-level build.gradle

repositories {
    jcenter()

    maven {
      url  "https://adcolony.bintray.com/AdColony"
    }
}

Dependencies{
     implementation 'com.google.ads.mediation:adcolony:4.1.4.1'
}

i got an error saying Task :app:transformClassesAndResourcesWithR8ForRelease FAILED. been looking on the internet, but no luck so far.

So i decided to do Manual Integration, which requires me to download adcolony.jar and adcolony-4.1.4.1, put the files on app/libs/ And wrote this on my app level build.gradle

Dependencies{
    implementation 'com.android.support:support-annotations:28.0.0'
    implementation fileTree(include: ['adcolony.jar'], dir: 'libs')
    implementation fileTree(include: ['adcolony-4.1.4.1.aar'], dir: 'libs')
}

I even give permission on this since google document says to make adcolony performs better

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.VIBRATE" />

Everything works and no error when building an app bundle. Today, I checked my Admob it says it sent over 2k request to adColony but got 0 impressions. And when I checked my adColony Dashboard, everything is 0. Do I miss something here?

Not sure if this is related while implementing adColony as mediation but there is this warning on my adColony Dashboard

Warning