$BeyondSpring (BYSI.US)$ I bought a put option for the Octob...

I bought a put option for the October 15 delivery month for 6.2 yuan. The stock price dropped by 4.2 yuan today and the option didn't increase. Why? If anyone understands, please let me know, OK? I just started buying options. If I don't have any knowledge, please let me know, thank you!