AdCOM Placement has no display, video, or audio subtype
item.spec.placement has none of the media subtype objects AdCOM requires.
What it means
An AdCOM Placement is the root of what an OpenRTB 3.0 item is selling. The spec marks display, video, and audio as required-star: at least one subtype object has to be present so a buyer knows which media the placement accepts.
Why it matters
A placement with only tagid or secure and no subtype is not a sellable impression. Buyers cannot match a creative to it, and an exchange that forwards it is offering an item with no allowed ad.
How to fix it
Add a display, video, or audio object under placement. A banner slot is placement.display; a preroll is placement.video with mime and duration bounds.
Example that trips it
{ "openrtb": { "ver": "3.0", "domainver": "1.0", "request": { "id": "req-1", "item": [{ "id": "1", "spec": { "placement": { "tagid": "plc-1" } } }] } } }tagid names the slot but does not say what can run in it. AdCOM wants at least one of display, video, or audio.
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.