Comfy-Org/ComfyUI · error · RuntimeError

Unexpected response: the first item is not the base image.

Error message

Unexpected response: the first item is not the base image.

What it means

Raised by ByteDanceSeedreamLayerSeparationNode when the first item's z_index is neither 0 nor 1,000,000 (the sentinel used for missing/unparseable z_index). The node requires the first item to be the base image; a non-base first item means the ordering contract of the response was violated.

Source

Thrown at comfy_api_nodes/nodes_bytedance.py:1262

            if isinstance(v, (int, float)):
                return int(v)
            if isinstance(v, str):
                try:
                    return int(v.strip())
                except ValueError:
                    return 1_000_000
            return 1_000_000

        data = [d for d in (response.data or []) if isinstance(d, dict)]
        if not data or "url" not in data[0]:
            raise RuntimeError("Unexpected response: no base image returned.")
        base_item = data[0]
        if base_item.get("bounding_box") is not None:
            logging.warning(
                "ByteDance layer separation: base item unexpectedly carries a bounding_box; ignoring it."
            )
        if z_index_of(base_item) not in (0, 1_000_000):
            raise RuntimeError("Unexpected response: the first item is not the base image.")
        layer_items = [d for d in data[1:] if "url" in d]
        dropped = len(data) - 1 - len(layer_items)
        if dropped > 0:
            logging.warning(
                "ByteDance layer separation: %d of %d returned elements had no 'url' and were dropped.",
                dropped,
                len(data) - 1,
            )
        if not layer_items:
            raise RuntimeError("The model returned no layers. Try a different prompt or input image.")
        layer_items.sort(key=z_index_of)

        base_image = (await download_url_to_image_tensor(str(base_item["url"])))[..., :3].contiguous()
        height, width = base_image.shape[1], base_image.shape[2]

        specs = []
        for item in layer_items:
            flags = []

View on GitHub (pinned to 1c6d8d45b3)

Solutions

1. Retry once — ordering anomalies can be transient.
2. Update ComfyUI to the newest version, since the z-index heuristics may have been updated for a new API behavior.
3. File a bug with the raw response from ComfyUI/temp/api_logs/ attached.

except RuntimeError as e:
    if 'first item is not the base image' in str(e):
        result = await separate_layers(image)  # one retry; ordering anomalies are often transient
        # if it repeats, report with api_logs payload
    else:
        raise

When it happens

Trigger: The API returns a layer (not the base) first, carrying an explicit z_index other than 0; z_index_of parses a value like 2 or 5 for data[0].

Common situations: BytePlus changes the ordering of returned items or adds new z_index semantics; a response contract change shipped server-side.

Related errors

• Unexpected response: no base image returned.
• Only a single input image is supported.
• The model returned no layers. Try a different prompt or inpu
• Failed to download layer {i + 1} of {len(specs)} (name={item
• Only {len(urls)} of {len(response.data)} images were generat

AI-assisted analysis of Comfy-Org/ComfyUI@1c6d8d45b3 (2026-08-14). Data as JSON: /api/errors/4cb0ebc1d656c43c. Report an issue: GitHub.