AdMobPlugin doesn't show..

Hello everyone, I have downloaded this plugin for admob:
AdMobPlugin

I put in the publisher id, I carried out all the instructions, but my phone will only charge “SMART_BANNER” everyone else does not show them.

is such a thing happened to you?
how have you solved it?

Thank you all for your time.

  • Ardito

When I want to display the banner I check this inscription:
ad request successful, but no ad returned to lack of ad inventory

I solved audience here the solution so that in the future it may be useful to someone else:
solution