I get this error when i am doing an update to my Ubuntu 20.4 operating system.
(Ubuntu 20.04.4 LTS (GNU/Linux 5.4.0-124-generic x86_64)
Err:4 https://apt.hestiacp.com focal InRelease
The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY A189E93654F0B0E5