Following install instruction I get the error message:

The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654

pi@raspberrypi:~ $ sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'

pi@raspberrypi:~ $ sudo apt-key adv --keyserver hkp://ha.pool.sks-keyservers.net:80 --recv-key 
421C365BD9FF1F717815A3895523BAEEB01FA116

Executing: /tmp/apt-key-gpghome.MdEqEf8EV4/gpg.1.sh --keyserver hkp://ha.pool.sks-keyservers.net:80 --recv-key 421C365BD9FF1F717815A3895523BAEEB01FA116

gpg: key 5523BAEEB01FA116: public key "ROS Builder <rosbuild@ros.org>" imported

gpg: Total number processed: 1

gpg:               imported: 1

pi@raspberrypi:~ $ sudo apt-get update && sudo apt-get upgrade -y 

Hit:1 http://raspbian.raspberrypi.org/raspbian buster InRelease

Hit:2 http://archive.raspberrypi.org/debian buster InRelease

Get:3 http://packages.ros.org/ros/ubuntu buster InRelease [4,633 B]

Err:3 http://packages.ros.org/ros/ubuntu buster InRelease

  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654
Reading package lists... Done

W: GPG error: http://packages.ros.org/ros/ubuntu buster InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654

E: The repository 'http://packages.ros.org/ros/ubuntu buster InRelease' is not signed.

N: Updating from such a repository can't be done securely, and is therefore disabled by default.

N: See apt-secure(8) manpage for repository creation and user configuration details.

Installing on a raspi3 with freshly installed Buster, it was working fine on Jessi. Can anyone help? Thx.