openrtb.native.request.unparseable
What it means
imp.native.request should contain a JSON-encoded Native Markup Request, but the string does not parse as JSON at all: truncated content, an unescaped quote, or something that was never JSON.
Why it matters
Native demand cannot bid on an impression whose asset requirements it cannot read. Because the outer bid request still parses, the breakage hides one layer down where generic JSON tooling does not look.
How to fix it
Serialize the Native Markup Request with a JSON library and validate the inner document as JSON before embedding it. The native reference covers the request's required structure per Native Ads 1.2.
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.