GPG error: http://ppa.launchpad.net/ondrej/php/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4F4EA0AAE5267A6C 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