Call when an agent needs current perpetual funding for one symbol or a fixed major list. Tries Hyperliquid and Binance USDT-M futures, then OKX and Bybit. Includes next funding time and mark or index when the venue returns them. A geo-blocked venue is skipped. Send JSON {"symbol":"BTC"}. Exact $0.002 USDC on Base. Try unpaid POST /v1/sandbox/perp-funding-rates first.