If the "argocd" configuration property is missing when the Argo CD plugin is enabled, the error below is printed in the backstage Pod logs.

This error message might seem innocuous, however it's confusing if someone believes they have configured the plugin correctly. In my case, I had placed the "argocd" key under the "app" in my app-config.yaml, i.e under the app.argocd key. As a result, I assumed my config was found, but the URL was malformed, or that the $env substitution was not working. 

In my case, the correct error is "The 'argocd' config property was not found" or similar. The URL error initially lead me to believe my "app.argocd" location was correct.

ForwardedError: Plugin 'app' startup failed; caused by Error: Invalid app bundle schema. If this error is unexpected you need to run `yarn build` in the app. If that doesn't help you should make sure your config schema is correct and rebuild the app bundle again. Caused by the following schema error, Error: Config validation failed, Config must have required property 'url' { missingProperty=url } at /argocd/appLocatorMethods/0/instances/0; Config must have required property 'url' { missingProperty=url } at /argocd/appLocatorMethods/0/instances/1