RTBlintAlpha
Native asset does not have exactly one of title, img, video, or data
A native asset has none of those subtypes, or more than one.
What it means
Native Ads 1.2 allows exactly one of title, img, video, or data on an asset. Link is additional on the response, not a substitute.
Why it matters
A buyer that sees both title and img on one asset, or neither, cannot tell which creative part to return. Exchanges reject mixed assets.
How to fix it
Split mixed assets into one object per subtype, each with its own id. Empty assets are not slots.
Example that trips it
{ "native": { "request": "{\"ver\":\"1.2\",\"assets\":[{\"id\":1}]}" } }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.