Your first generation Pencil can only be paired with (or charged by) your iPad10 using the USB-C cable and special USB-C to Lightning adapter.
New first generation Pencils sourced from Apple should ship with this special adapter in the box along with the Pencil. Some older stock, purchased from retailers, may lack the USB-C to Lightning adapter - and may instead have an older Lightning to Lightning Adapter that looks very similar.
USB-C to Apple Pencil AdapterFor owners of older first generation Pencils, or for “old stock” new Pencils, the new special adapter can be purchased directly from Apple as an accessory.
https://store.apple.com/uk/xc/product/MQLU3ZM/A