$S&P 500 Index(.SPX.US)$  is a stock index that provides information on the performance of a basket of securities so you cannot trade SPX directly.
https://www.thebalance.com/trading-stock-indexes-1031061
https://www.investopedia.com/ask/answers/how-can-i-buy-sp-500-fund/
There are ETFs that track SPX like   $SPDR S&P 500 ETF(SPY.US)$   $iShares Core S&P 500 ETF(IVV.US)$   $Vanguard S&P 500 ETF(VOO.US)$   $SPDR Portfolio S&P 500 ETF(SPLG.US)$ $SPDR S&P500 US(S27.SG)$ and these...