Why isn’t my Apple Pencil generation one working?

This support page may be helpful with pairing and use of the Pencil with your iPad:

Connect Apple Pencil with your iPad - Apple Support

If you continue to experience difficulties, here is one of the better troubleshooting guides:

https://appletoolbox.com/apple-pencil-not-working-heres-our-troubleshooting-guide/

Ensure that the Pencil tip is firmly screwed into place. Even if slightly loosened, this can affect performance.

What iPad year and model are you using the 1st gen Pencil with?

Is this a new Pencil purchase?

Prior to this issue, when was the last time your Pencil was charged up and used with your iPad?