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HTTP status: 400 · Title: “Outcome index invalid”

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When it fires

outcomeIndex is negative, or greater than or equal to the market’s number of outcomes. Returned by POST /v1/trades, GET /v1/markets/{id}/quote and POST /v1/redemptions.

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Why it happens

  • You hard-coded outcomeIndex: 1 assuming a binary market and pointed it at a market with a different shape.
  • Off by one: the field is zero-indexed. The first outcome is 0, not 1.
  • The index was computed from a label without a bounds check.

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How to fix

  • Fetch the market with GET /v1/markets/{id} and check outcomes.length. The valid range is 0 to length - 1.
  • Map outcome labels to indices once when you fetch the market, then use the index throughout your code.