Why is Apache cordova's cordova-plus-admob plugin not working?

Question

I am using cordova-plus-admob plugin in my apache cordova app, but the plugin is not showing ads. Also, there is no error in the console. I am trying to start Admobu but it is not giving any response.I did all the admob installations.

document.addEventListener("deviceready", () => {
  admob.start().then(() => {
    console.log("ADMOB STARTED");
  }).catch(err => {
    console.error(err);
  });
});