Try charging the Pencil longer, like a couple of hours.
The battery may have been flat ( 0% charged ) or close for too long.
If no joy after charging for 2-3 hours, your Apple Pencil battery has failed and your Apple Pencil is dead.
If your Apple Pencil sat around unused and not kept charged up for more than a few weeks, or so, OR LONGER, then the battery in your Apple Pencil may have failed and is dead and you will have to purchase another brand new Apple Pencil.
Sorry.
FYI and something Apple never divulges to it potential iPad Pro/Apple Pencil customers/users unless the potential customer/user is smart enough to ask about.
Due to the “always on and active/standby” nature of the Apple Pencil and, also, due to its very tiny rechargeable Li-ion battery (smaller than the eraser head on a REAL wooden pencil), the Apple Pencil needs to be constantly charged up to some significant charge level ALL THE TIME, even when not using the Pencil for prolonged periods of time.
The Apple Pencil needs to be kept charged to a minimum of 5-10% all the time.
If the Apple Pencil battery is allowed to drain down to 0% and allowed to stay in that flat condition for more than a few weeks, or so, OR EVEN LONGER, that very tiny little Li-ion battery is too small to keep at a 0% state for a long period of time and it will fail and the Apple Pencil will be dead and you may have to “pop” for another $99 Apple Pencil, once again!