AI music negative prompt: why the API returns 400

A negative prompt does not work on Sume's music API: a non-empty negative_prompt returns HTTP 400 with public_reason=negative_prompt_unsupported. The docs say Music 1.0 and Lyria do not support negative prompting, so omit the field, or send an empty string, and write what you want to avoid into the positive prompt.

From the Music 1.0 and Music Router docs, read 2026-09-29.

What does a working request look like?

Move each exclusion into the prompt as a clause. The example below excludes vocals and drums.

curl -X POST https://api.sume.com/v1/music-router/generate \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: exclusions-001" \
  -d '{
    "prompt": "Ambient piano and pad, 60 BPM, A minor. A 1-minute track. No drums, no vocals, no spoken word."
  }'

Which other fields are rejected?

Do exclusions always work?

Not always. The docs call prompt directions creative guidance, not guaranteed settings, so listen to each take. If an unwanted element appears, restate the exclusion more plainly and generate again; each take is a billed generation.