This could arise due to network, software, or hardware issues and sometimes due to incompatibility.
Check for Compatibility
The first thing we need to check is the compatibility, different generation pencils are compatible with different devices. Make sure you are researching before buying the Apple Pencil.
Reconnect the Apple pencil
Apple pencil uses Bluetooth to connect, so turn it off and on once to refresh the connection. Reconnect by switching on the Bluetooth.
Charge the pencil
This might be due to a low charge on the pencil, charge the pencil and try again to connect. Charge it using the iPad.
Forget as a Bluetooth device
Re-establish the Bluetooth connection by forgetting the device on Bluetooth, go to the settings, and forget. Make a connection and check again.
Remove faulty apps and update
Faulty apps can also be a reason, identify them while using the iPad. Remove them and update the already-using apps to resolve the issue.
Reset all the settings
Network and cellular settings also need to be reset. Go to the reset all settings and confirm the action to reset all the connections.
Contact Apple Customer Support
The last thing you can try is contacting customer support, checking the details of your problem online, and connecting with Apple.