Hi,
Its because you used some incorrect commands.
Dont need to change the $DISTRO in the commands, its a variable.
You can try reverting your action with following commands:
echo "" > /etc/apt/sources.list.d/apt-radxa-com.list # to blank out current file contents
export DISTRO=stretch
echo "deb http://apt.radxa.com/$DISTRO/ ${DISTRO%-testing} main" | sudo tee /etc/apt/sources.list.d/apt-radxa-com.list # this is the default
sudo apt-get update
Then try re running correct command for testing repo add:
export DISTRO=stretch-testing
echo "deb http://apt.radxa.com/$DISTRO/ ${DISTRO%-testing} main" | sudo tee /etc/apt/sources.list.d/apt-radxa-com.list # testing repo for bluetooth
wget -O - apt.radxa.com/$DISTRO/public.key | sudo apt-key add -
sudo apt-get update
And then follow the commands here to install the bluetooth patch: