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

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When it fires

outcomeIndex is greater than or equal to the market’s outcome count, or negative.

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Why it happens

  • You hard-coded outcomeIndex: 1 (assuming a binary market) and pointed at a multi-outcome market.
  • Off-by-one: the field is zero-indexed — first outcome is 0, not 1.
  • A bug computed the index from a label without bounds-checking.

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How to fix

  • Look up the market via GET /v1/markets/:id and check outcomes.length — valid range is [0, length - 1].
  • Map outcome labels to indices once when you fetch the market, then use the index throughout your code.