NO_PUBKEY F1656F24C74CD1D8, Ubuntu 18

Problem:

# apt update
Get:1 http://mirrors.digitalocean.com/ubuntu bionic InRelease [242 kB]
Hit:3 http://mirrors.digitalocean.com/ubuntu bionic-updates InRelease
Hit:4 http://mirrors.digitalocean.com/ubuntu bionic-backports InRelease
Get:2 http://archive.mariadb.org/mariadb-10.3.17/repo/ubuntu bionic InRelease [3887 B]
Get:5 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]
Hit:6 http://repo.zabbix.com/zabbix/4.2/ubuntu bionic InRelease
Err:2 http://archive.mariadb.org/mariadb-10.3.17/repo/ubuntu bionic InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F1656F24C74CD1D8
Reading package lists... Done
W: GPG error: http://archive.mariadb.org/mariadb-10.3.17/repo/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F1656F24C74CD1D8
E: The repository 'http://archive.mariadb.org/mariadb-10.3.17/repo/ubuntu bionic InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Solution:

sudo apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 F1656F24C74CD1D8