Required Native Ads field is missing
A Native Ads field the spec marks required is absent: title.len, data.type, video mimes/protocols/duration, eventtracker event/methods, or response text/url/vasttag/value/link.url.
What it means
After decoding the native string, a required inner field is missing. On the request that is title.len, data.type, video.mimes, video.protocols, video.minduration, video.maxduration, and eventtrackers.event plus methods. On the response that is link.url, title.text, img.url, video.vasttag, and data.value.
Why it matters
Those fields are how the other side sizes a title, picks an image, or follows a click. Missing them is a dropped native bid, not a style warning.
How to fix it
Populate the field named in the path. Video native assets need the same four fields as a standalone Video object.
Example that trips it
{ "native": { "request": "{\"ver\":\"1.2\",\"assets\":[{\"id\":1,\"title\":{}}]}" } }title is present but len is not. Native Ads 1.2 makes title.len required.
Check your payload
Paste a bid request or response into the tester to see whether this code fires against it, or gate on the id in CI with the CLI: the id is stable, wording is not.
Back to the full diagnostic code reference.