react-native-admob: Banner does not show on real iOS devices

I always get

Error: Request Error: No ad to show.

Is anyone having the same problem?

Tests: Android emulator: ok Android real device: ok iOS emulator: ok iPhone 8: banner won’t show iPhone 5c: banner won’t show (edited) iPhone 8 Plus: ok

Using react-native 0.47.1 and the latest commit of this library

import { AdMobBanner } from 'react-native-admob';

export default class MyAdMobBanner extends Component {
  render() {
    return (
      <View style={{ alignItems: 'center' }}>
        <AdMobBanner
          adSize={'smartBannerPortrait'}
          adUnitID={myID}
          onAdFailedToLoad={er => console.log(er)}
        />
      </View>
    );
  }
}