Unable to run successfully e01_basic_ping_bot

[lorenzo111111]

I was trying to run the example 1 (see title), but I was unsuccessful.
I set the DISCORD_TOKEN correctly and initialization seems successful. However, when I receive a "!ping" message I got the following error:
Error sending message: Http(UnsuccessfulRequest(ErrorResponse { status_code: 401, url: "https://discord.com/api/v10/channels/1205198741049708545/messages", method: POST, error: DiscordJsonError { code: 0, message: "401: Unauthorized", errors: [] } }))

[jamesbt365]

Your bot doesnt have permissions to send messages in that channel.

[lorenzo111111]

Your bot doesnt have permissions to send messages in that channel.

How can I solve?