Spot-Futures Arbitrage bot can get profit in either bullish or bearish. Spot-Futures Arbitrage bot is having the spot cryptocurrencies and the short contracts at the same time to earn the funding fee. Funding fee is your investment multiplied with the funding rate.
The funding rate ensures that futures prices and index prices converge regularly.
So when a perpetual futures contract is trading on a premium (higher than the spot markets), long positions have to pay shorts due to a positive funding rate.
In contrast, short positions pay longs while the futures price is trading below the index price.
The Index Price consists of the average price of an asset, according to major spot markets and their relative trading volume.