Using ${applicationId} in library manifest

You can use ${applicationId} in under manifest file. Just make sure that in your gradle file of that library doesn't have "applicationId". If you declared it in your gradle file under "defaultConfig", please remove it.

//So your gradle file of library(SDK) module looks like..

defaultConfig {
minSdkVersion Version.minSdk
targetSdkVersion Version.targetSdk
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
} 


//And your application gradle file looks like..

defaultConfig {
    applicationId "com.example.android"
    minSdkVersion Version.minSdk
    targetSdkVersion Version.targetSdk
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
 }

Was running into the same problem with several different variants and unique IDs, and ended up going with replacing a placeholder key when Gradle is building the app, kind of like so:

Gradle 3+

android.applicationVariants.all { variant ->
    variant.outputs.each { output ->
        output.processManifest.doLast {
            File manifestFile = file("$manifestOutputDirectory/AndroidManifest.xml")

            replaceInFile(manifestFile, 'P_AUTHORITY', variant.applicationId)
        }
    }
}

def replaceInFile(file, fromString, toString) {
    def updatedContent = file.getText('UTF-8')
            .replaceAll(fromString, toString)

    file.write(updatedContent, 'UTF-8')
}

Gradle < 3

android.applicationVariants.all { variant ->
    variant.outputs.each { output ->
        output.processManifest.doLast{
            replaceInManifest(output, 'P_AUTHORITY', variant.applicationId)
        }
    }   
}

def replaceInManifest(output, fromString, toString) {
    def manifestOutFile = output.processManifest.manifestOutputFile
    def updatedContent = manifestOutFile.getText('UTF-8').replaceAll(fromString, toString)
    manifestOutFile.write(updatedContent, 'UTF-8')
}

And then in the manifest:

<provider
    android:name=".core.MyContentProvider"
    android:authorities="P_AUTHORITY"
    android:exported="false"/>

That's come in handy quite a few times