NEED AN URGENT UPDATE (NOT WORKING)

[akaoppa]

I'm receiving everytime now : ERROR Advert failed to load native: {"code": 3, "domain": "com.google.android.gms.ads", "message": "No fill."}
or
ERROR Advert failed to load: [Error: [googleMobileAds/error-code-no-fill] The ad request was successful, but no ad was returned due to lack of ad inventory.]