Hi,
We have fixed that issue with this guide.
Step 1: Get tool wget
sudo apt update
sudo apt-get install -y wget
Step 2: Edit /etc/apt/sources.list.d/apt-radxa-com.list
deb http://apt.radxa.com/buster-stable/ buster main
deb http://apt.radxa.com/buster-testing/ buster main
Step 3: Get the public key
wget -O - apt.radxa.com/buster-testing/public.key | sudo apt-key add -
wget -O - apt.radxa.com/buster-stable/public.key | sudo apt-key add -
Step 4: Test
sudo apt update
sudo apt install -y linux-4.4-rock-pi-e-latest