Interstitial Admob ads: "IllegalStateException: Only fullscreen activities can request orientation"

EDIT

Now a newer admob version is available. I confirm that using the latest releases (15.0.1 or newer) the issue doesn't appear anymore, so you can use the latest version of Admob

com.google.firebase:firebase-ads:17.1.2

setting the target version to the latest, if you have used the workaround previously suggested.

----------------------------------------------------------

Set the target to Android API Level to 26 to fix the issue, waiting for Admob update

In build.gradle

targetSdkVersion 26

if targetSdkVersion is >=27 ( > android.os.Build.VERSION_CODES.Othat is 26) you get this error, they have changed ActivityRecord in latest Android version adding this:

void setRequestedOrientation(int requestedOrientation) {
        if (ActivityInfo.isFixedOrientation(requestedOrientation) && !fullscreen
                && appInfo.targetSdkVersion > O) {
            throw new IllegalStateException("Only fullscreen activities can request orientation");
        ....
        }

The change has been introduced in this commit

Prevent non-fullscreen activities from influencing orientation This changelist enforces that activities targeting O and beyond can only specify an orientation if they are fullscreen.

and probably in admob lib have messed some check

try to add this in your manifest

<activity
android:name="com.google.android.gms.ads.AdActivity"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen"
tools:replace="android:theme"
 />

Or, if you are using appcompat:

<style name="TranslucentTheme" parent="@style/Theme.AppCompat.Light.NoActionBar">
    <item name="android:windowNoTitle">true</item>
    <item name="android:windowActionBar">false</item>
    <item name="android:windowFullscreen">true</item>
    <item name="android:windowContentOverlay">@null</item>
    etc

And in the manifest, make sure the activity is declared with

android:theme="@style/TranslucentTheme"

please do not use any properties in Android Manifest files AdActivity.

please remove this line from AdActivity in Manifest file

android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"

Just simply add this following line to Android Manifest file.

    <activity android:name="com.google.android.gms.ads.AdActivity" />

If you want to set your desired activity as portrait mode please add this following line to your activities onCreate method:

if (android.os.Build.VERSION.SDK_INT != Build.VERSION_CODES.O) {
   activity.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
}

For firebase ADS 17.0.0 and upper versions use this line to manifest file.

<application
...........>

    <meta-data
        android:name="com.google.android.gms.ads.APPLICATION_ID"
        android:value="@string/app_id" />

</application>

You can get app id from Admob -> Apps -> your app -> App Settings -> App Id. Please copy and paste this App_Id into your project.