The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A1715D88E1DF1F24 code example

Example 1: 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

Example 2: he following signatures couldn't be verified because the public key is not available: NO_PUBKEY 363A96A5CEA9EA27

sudo apt-key adv --keyserver ha.pool.sks-keyservers.net --recv-keys 363A96A5CEA9EA27