Why do KivMob Test ads show but my ads don't in Kivy?

I'm trying to show real ads with KivMob in my mobile kivy application (python)

I've created

1. An AdMob account
2. A new app
3. An ad unit (interstitial)
4. A test device in AdMob (with an add recognizer i found in google settings in this device)

In my python code I then call these functions:

self.ads = KivMob('my publisher id')
self.ads.add_test_device('my device id') # 16 characters long?
self.ads.new_interstitial('my interstitial add unit id') 

Then when i need to show the add I simply do:

self.ads.request_interstitial()
self.ads.show_interstitial()

This particular code works perfect when I use KivMob's TestIds like this

self.ads = KivMob(TestIds.APP)
self.ads.new_interstitial(TestIds.INTERSTITIAL)

instead of my ids

self.ads = KivMob('my publisher id')
self.ads.add_test_device('my device id') # 16 characters long?
self.ads.new_interstitial('my interstitial add unit id') 

If i specify those id's no ads show up. Why is that? Am I doing something wrong?