You don’t have a sub panel. You only have a main panel. Does it look like this?
https://www.bing.com/images/search?q=breaker+panels+residential&qpvt=breaker+panels+residential&form=IGRE&first=1&cw=1117&ch=493
https://www.bing.com/images/search?q=breaker+panels+residential&qpvt=breaker+panels+residential&form=IGRE&first=1&cw=1117&ch=493