You were advised wrong. The First generation Apple Pencil is not compatible with an iPad Pro at all.
iPad Pro 12.9" 3rd gen and later and 11" , require a Second Generation Apple Pencil.
The Fist Generation Apple Pencil uses the adapter to work with the 10th Generation regular iPad.
Click here ➜ Apple Pencil compatibility - Apple Support
Apple Pencil (2nd generation)
You can use Apple Pencil (2nd generation) with these iPad models:
- iPad mini (6th generation)
- iPad Air (4th generation and later)
- iPad Pro 12.9-inch (3rd generation and later)
- iPad Pro 11-inch (1st generation and later)
Apple Pencil (1st generation)
You can use Apple Pencil (1st generation) with these iPad models:
- iPad mini (5th generation)
- iPad (6th, 7th, 8th, and 9th generation)
- iPad (10th generation)*
- iPad Air (3rd generation)
- iPad Pro 12.9-inch (1st and 2nd generation)
- iPad Pro 10.5-inch
- iPad Pro 9.7-inch
* You need the USB-C to Apple Pencil Adapter to pair and charge Apple Pencil with iPad (10th generation).