Hi there,
I think the issue you are seeing is caused by the default security settings in Strapi. By default, the plugins are only allowed to connect to secure URLs with https and your Chartbrew instance is running locally on http
I wrote a quick guide on how to change these settings over here: GitHub - chartbrew/strapi-plugin-chartbrew: The official Strapi plugin that integrates Chartbrew charts in the Strapi dashboard
Let me know how it goes 