Bidding network wins auction but fails to serve ad – no fallback

[Ronald Geisler]

Hi

I'm experiencing an issue with mediation involving Meta Audience Network as a bidding partner. Meta frequently wins the auction via bidding but then fails to deliver an ad (“No Fill”). In these cases, the ad slot remains empty, even though I have other networks (e.g., AdMob, Unity) configured in the waterfall that could have provided a valid fill.

From my understanding, if a bidding partner fails to deliver an ad after winning the auction, there should ideally be a fallback to another eligible network. However, this fallback does not occur, and the opportunity is lost.

My questions:

1. Is this behavior expected by design?

2. Is there a way to allow fallback to other networks when the winning bidder returns a "No Fill"?

3. If not, are there any best practices you recommend to avoid revenue loss in such cases (e.g., implementing a manual fallback in code)?

Thank you for your help and clarification on this matter.

I use:

implementation 'com.google.android.gms:play-services-ads:24.4.0'

implementation 'com.google.ads.mediation:facebook:6.20.0.0'
implementation 'com.unity3d.ads:unity-ads:4.15.1'
implementation 'com.google.ads.mediation:unity:4.15.1.0'
implementation 'com.google.ads.mediation:applovin:13.3.1.1'
implementation 'com.google.ads.mediation:ironsource:8.10.0.0'

Best regards,

Ronald

[Mobile Ads SDK Forum Advisor]

Hi,

Thank you for contacting the Mobile Ads SDK Support team.

The Error code 3, no fill error means that the ad request was successful, but no ad was returned due to lack of ad inventory. You may check this AdMob Error Codes & Logs for more information on different kinds of errors.

Once the ad request is matched to a mediation group, the bidding ad sources in the group compete in an auction to fill the request. If a bidding ad source is placed first in the mediation waterfall, it will get the opportunity to serve the ad. If a bidding partner wins but fails to deliver, AdMob does not automatically try other networks. Kindly check the Mediation bidding documentation  and AdMob Mediation for more information. For best practices i would suggest to implement Manual retry on load failures with some limit.

Please note that when testing, ensure that you have the Facebook app installed on the test device and be logged in with a valid Facebook login. See Meta's documentation for more details. Without this, it is expected that Facebook might not bid (though they still might get bid requests). If issue still persists,Could you kindly provide the below information via reply to author option for further investigation:

• app ID
• ad unit ID

 

Thanks,
 

Mobile Ads SDK Team

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[2025-07-14 14:18:32Z GMT] This message is in relation to case "ref:!00D1U01174p.!500Ht01svXdh:ref" (ADR-00318804)

[Ronald Geisler]

Thank you for your response.

I understand that Error Code 3 indicates a successful ad request with no available inventory. However, I’d like to highlight that in my case, Meta Audience Network consistently wins the bidding auction, even when testing on devices without the Facebook app installed, or within emulators – and then fails to deliver any ad content. Despite this, AdMob does not fall back to other networks in the mediation group, which results in an empty ad slot.

Based on your recommendation, I will now implement a manual fallback. I will load a secondary AdMob-only ad unit to avoid losing the impression opportunity.

I’ll observe this behavior in the upcoming release and continue monitoring its impact on performance.

Thanks again for your assistance.