It's been a little while since I set Admob up as I don't use it for my newest apps, but I don't think it will show live adverts until you have set up a store listing and published it. In the Admob admin website if you go to your app and choose "App settings" you need to give it the "App store details" and it says "To make sure setup is complete and your app is ready to show ads, you must add one or more app stores and provide the store details for this app".
According to their help pages, before it will show live ads:
Your app must be published and available to end-users.
Your app must be listed in a supported store (so basically Google Play or Apple's App Store).
Your app must be set up correctly in AdMob and linked to a supported store.
Until it meets all three criteria then your app won't show real adverts. I think it has to be approved by them too to ensure it meets their rules, so there will be a delay before the ads appear. It is sort of a blind
"wait and see if everything actually works" kind of situation when you turn off test ads and publish your app.
The full help info is here:
https://support.google.com/admob/answer/10564477?hl=en
