Native enum value is not in the documented set
data.type, img.type, eventtrackers.event, or methods carries a value Native Ads does not list (and it is below the vendor range 500+).
What it means
Native Ads publishes small integer lists: image types 1 (icon), 2 (logo), 3 (main); data types 1-12; event 1-4; methods 1-2. Values 500 and above are exchange-specific and allowed.
Why it matters
An undocumented type is not a custom creative. Buyers that switch on the enum skip the asset or the whole impression.
How to fix it
Use a documented value, or 500+ if the exchange published a private type. Do not invent 13 for a thirteenth data type.
Example that trips it
{ "native": { "request": "{\"ver\":\"1.2\",\"assets\":[{\"id\":1,\"data\":{\"type\":99}}]}" } }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.