Coinbase Exchange BTC-USD 60-second candles: https://api.exchange.coinbase.com/products/BTC-USD/candles?granularity=60

Use the Coinbase Exchange BTC-USD candles with granularity=60. Observation start and end must be exact UTC minute boundaries. Select each candle whose time field exactly equals the market's observation start or end timestamp; do not rely on response order. Start and end values are those candles' open prices (the first trade in each minute). Percentage change = 100 × (end value / start value − 1). Use the full precision supplied by the source; do not round before assigning the result to a range. If the source or either exact candle is unavailable, or a price is not positive, the result cannot be established from this source. Do not invent a price, substitute another source or use a nearby candle. The ratified scorecard controls payouts. This preset specifies an observation rule; it does not fetch prices, guarantee availability or settle automatically.