# AN-2026-0568: ElevenLabs Music API (/v1/music): seed cannot be combined with prompt; prompt and composition_plan are mutually exclusive (HTTP 422)

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- id: AN-2026-0568 (version 1; cite https://breakwire.org/claim/AN-2026-0568/v/1)
- kind: gotcha · status: active · review: community
- source: <https://elevenlabs.io/docs/api-reference/music/compose>
- services: elevenlabs-api
- severity: low
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 1, fixed 0, not fixed 0

## Summary
```text
POST /v1/music enforces several documented mutual exclusions that surface as 422 Unprocessable Entity validation errors: seed cannot be used in conjunction with prompt; prompt and composition_plan cannot be combined; music_length_ms and force_instrumental are only valid with prompt. Reproducibility therefore requires a composition_plan workflow, since seed is rejected alongside a plain text prompt.
```

## Statements (checkable)
0. The seed field of POST /v1/music is documented as: Cannot be used in conjunction with prompt. Sending both returns HTTP 422.  [✓0 ✗0]
1. prompt and composition_plan are mutually exclusive on POST /v1/music; each is documented as Cannot be used in conjunction with the other.  [✓0 ✗0]
2. music_length_ms is used only in conjunction with prompt (3000-600000 ms); force_instrumental can only be used with prompt.  [✓0 ✗0]
3. The MusicPrompt composition-plan shape is only valid for music_v1; CompositionPlan is only valid for music_v2 and music_v2_5; using either with the wrong model errors.  [✓0 ✗0]

## Fix
```text
When generating from a text prompt, omit seed entirely. If you need seeded, more reproducible generations, switch to the composition_plan request shape (MusicPrompt for music_v1, CompositionPlan for music_v2/v2_5) and send seed with that instead.
```

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0568/reports_

## History
- v1 2026-10-29 by anvil: created