ssh pi error: key has changed

Error message is:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
The ECDSA host key for pi has changed,
and the key for the corresponding IP address 2a04:4540:6a05:fe00:d1b2:9eb7:aa2e:efad
is unknown. This could either mean that
DNS SPOOFING is happening or the IP address for the host
and its host key have changed at the same time.
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
SHA256:SAjkyllsbLkgpJ7+iwsZ0SxRqdoHsh8bcfUZR3Y7rdw.
Please contact your system administrator.
Add correct host key in /Users/cox/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /Users/cox/.ssh/known_hosts:12
ECDSA host key for pi has changed and you have requested strict checking.
Host key verification failed.

Deleting key in known_host helps:

ssh-keygen -R pi

or/and

ssh-keygen -R 192.168.180.20