Comment 6 for bug 1936281

So I got this to work without a problem. I think this is the fact you're trying to deploy the source of the charm, _not_ the build artifact.

    git clone --depth 1 https://github.com/canonical/alertmanager-operator.git
    cd alertmanager-operator
    charmcraft build
    cd -

    cat bundle.yaml
    bundle: kubernetes
    applications:
    alertmanager-k8s:
        charm: ./alertmanager-operator/alertmanager-k8s.charm
        scale: 1
        resources:
        alertmanager-image: "ubuntu/prometheus-alertmanager"

    juju bootstrap microk8s mk8s
    juju deploy ./bundle.yaml

Hope this helps.