If the plastic tip broke off inside of that Pencil, you need to find a way to get that piece out of there.
That piece still left in there is preventing the metal tip in the Pencil tip from making contact with the Pencil’s metal transducer tip to be able to make electrical contact to function.
Failing that, IF your Pencil is still under its free, one-year warranty, You need to search online for your nearest, “local” Apple store location and call contact phone numbers and call to make an appointment to have your Pencil replaced with another new Pencil.
Good Luck to You!