Facebook Audience Network No fill Error when I put my Placement ID

When i keep my placement id Blank I mean I kept it default

Code (CSharp):

1. this.adView = new AdView("YOUR_PLACEMENT_ID", AdSize.BANNER_HEIGHT_50);

then it shows the add perfectly for all types. but when i put my placement id then it shows me fill error.
After putting my placement my code looks like.

Code (CSharp):

1. this.adView = new AdView("12345677_988776786", AdSize.BANNER_HEIGHT_50);

I am testing this with their samples. I am also getting an error in the logcat something like this "You dont call AudiencenetworkAds.Initialize(), for this Fan may not work properly". but this dont effect the add loading when i keep the placement to "YOUR_PLACEMENT_ID".
When I tried to initialize this i can't find anything like that

Looking for a solution.

NB: I have facebook app installed, My FAN project is approved by facebook, I have put the project on Test and Live mode for testing, I tested in emulator and also real divices with different facebook id logged in and also the test Id logged in.

 

Do you have a call to initialise somewhere? Seems like something obvious to try.

 

Did you find any solution i have the same issue