As per your concern, we want to inform you that the slot on the back of your tablet is for charging it. Whenever you put the pen in the slot, it automatically charges the S Pen. When it needs a charge, place the S Pen in the designated slot on the back of the tablet.
To check the current battery level for the S Pen Unlock the tablet’s lock screen and simply press the Pen button on the side of the S Pen while the pen is attached to the charging slot.
If you are facing any issues regarding not charging the S Pen, kindly visit the service center for a physical inspection of the product. You can locate your nearest service center with this given link: https://www.samsung.com/in/support/service-center/
Spen in galaxy tab s9 plus FE won't charge cause it doesn't need to be charged because it doesn't have any bluetooth functions. So it's not any issue...
