Response-native-admob is not showing any ads

Here is my code. But it only displays two red dots. No bugs etc. Any ideas what is wrong? Thanks to

... import {
    AdMobBanner,
} from 'react-native-admob'

export default class AboutApp extends Component {

    constructor(props) {
        super(props);
    }

    render() {
        return (
            <View style ={styles.container}>

                <AdMobBanner
                    bannerSize="fullBanner"
                    adUnitID="ca-app-pub-7257084341937***/7776***"
                    testDeviceID="EMULATOR"
                    didFailToReceiveAdWithError={this.bannerError} />
            </View>
        );
    }
}