Err:6 http://deb.playonlinux.com stretch InReleaseThe following signatures couldn't be verified because the public key is not available: NO_PUBKEY 73F0D6E88E3D6C3A 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