Java.Lang.SecurityException: in Maps

Hi im new and want to try out a Map on a Content page. And i get only a error with Java.Lang.SecurityException:

<ContentPage.BindingContext>
    <viewModel:MapModel/>
</ContentPage.BindingContext>
<ContentPage.Content>
    <StackLayout>
        <maps:Map WidthRequest="320" HeightRequest="200"
              IsShowingUser="true"
              MapType="Hybrid"
              VerticalOptions="Start"
              HorizontalOptions="FillAndExpand"/>         
    </StackLayout>
</ContentPage.Content>

package="com.companyname.FirstApp" android:installLocation="auto">
        <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="27" />
        <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
        <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
        <uses-permission android:name="android.permission.ACCESS_LOCATION_EXTRA_COMMANDS" />
        <uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION" />
        <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
        <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
        <uses-permission android:name="android.permission.INTERNET" />
        <application android:label="FirstAPP.Android">
            <meta-data android:name="com.google.android.maps.v2.API_KEY" android:value="NOT_PUBLIC" />
        </application>

I have no idea what are the Problem. Can you Help me?