A public key fingerprint is a short sequence of bytes used to identify a longer public key. Fingerprints are created by applying a cryptographic hash function to a public key.

If you ignore this blank, the SSH connection to your monitored host is vulnerable to a man-in-the-middle attack.

Fingerprints can be determined using ssh-keygen on your monitored host:

ssh-keygen -lf /etc/ssh/ssh_host_ecdsa_key.pub