Juju bootstrap: failed to verify certificate

I have a K0S cluster on which I attempt to exectute juju bootstrap like described here: https://juju.is/docs/olm/get-started-with-juju#heading--install-a-juju-controller-in-your-cloud

The very first command - juju bootstrap - fails with the following message:

ERROR juju.cmd.juju.commands bootstrap.go:968 unable to contact api server after 1 attempts: tls: failed to verify certificate: x509: certificate signed by unknown authority (possibly because of "crypto/rsa: verification error" while trying to verify candidate authority certificate "juju-ca")

I am not sure what is going on. I even tore down the whole Kubernetes cluster and re-deployed it to no avail. I tried to delete the local juju files in my home. Any hints as to why this happens and how I could solve it would be appreciated!