The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FEEA9169307EA071 NO_PUBKEY 8B57C5C2836F4BEB code example

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

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6494C6D6997C215E