The yaml examples for configuring the NotificationsConfiguration CR are incorrect as follows

spec:
 Services: 

Should be:

spec:
  services:  

Also

spec: 
  Subscriptions:  

Should be

spec: 
  subscriptions:  

Additionally, in the example to configure a service, it refers to $slack-token where according to the upstream docs (https://argo-cd.readthedocs.io/en/stable/operator-manual/notifications/services/slack/), it appears this is a placeholder to a key that should be in a k8s secret named "argocd-notifications-secret". The secret "argocd-notifications-secret" is managed by ArgoCD but there is no mention in the documentation of how these kinds of placeholders should be added to this secret.