Custom Native Ads Viewability metrics

[Antonio C]

Hello,

I'm trying to register the following metrics in the reporting for our Custom Native Ad Format ads on iOS and Android:

- Active View % measurable impressions  
- Active View % viewable impressions  

These metrics are reported correctly for our banner ads but not for our Custom Native Ad Formats.  

I understand that the GAM SDK handles impression tracking for banner ads, while for Custom Native Ads, we must implement our own impression tracking. We've done this successfully, and impressions are being counted for these ads. However, the Active View metrics remain at 0.  

The only reference to viewability for Custom Native Ad Formats I've found in the GAM documentation is the section on Open Measurement:  
[https://developers.google.com/ad-manager/mobile-ads-sdk/ios/custom-native-omid](https://developers.google.com/ad-manager/mobile-ads-sdk/ios/custom-native-omid)  

Is Open Measurement the only way to record Active View metrics for Custom Native Ads, or is there another method? Have others successfully recorded these viewability metrics for Custom Native Format ads on mobile? If so, could you share how?  

Thank you!