Music router 400 negative_prompt_unsupported: the fix and its cost

A non-empty negative_prompt on Sume's music router fails with 400 negative_prompt_unsupported; omit the field or send an empty string and put the exclusions in the positive prompt. The flat price is $0.125 per music generation, and a request that fails validation does not produce one.

Before and after

Same intent, two bodies. The first is rejected, the second is accepted.

Fixed request

Fold the exclusions into the last sentence of the prompt.

{
  "model": "sume/music-auto",
  "prompt": "Upbeat acoustic pop, 110 BPM, G major. Strummed guitar, handclaps. A 30-second track. Instrumental, no vocals, no drums.",
  "metadata": {"scene": "intro"}
}

Gotchas

Wrappers that always forward a negative_prompt default (for example from a shared image config) trip this error on every call. Strip the field for music. Also remember that unknown model ids return 400 model_not_found with a catalog_url; list valid ids with GET /v1/music-router/models.