openrtb.imp.media_type.required
What it means
An entry in imp[] carries none of banner, video, audio, or native. Those subordinate objects are how an impression declares what kind of creative is for sale; an imp without any of them offers nothing.
Why it matters
A bidder has no idea what creative form is acceptable, so it cannot bid. This usually comes from a request builder that attaches media objects conditionally and has a code path where every condition is false.
How to fix it
Attach the media object matching the placement, with its own required fields populated (for example video.mimes, or banner dimensions via w/h or format). An imp may offer several media types at once; it must offer at least one.
Example that trips it
{ "imp": [{ "id": "1", "bidfloor": 1.2 }] }A floor with nothing for sale behind it.
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.