I have started developing Power BI Custom Visualizations provided by Microsoft at the following link. develop-power-bi-visuals
However, I came across an issue when trying to debug the custom visualization using the Power BI Service.
I would create the basic template visual using pbiviz.new [ProjectName]. I could package and import the basic visual into either PBI Desktop or Web.
However, when I wanted to debug in web using the Developer Visual explained in this link set-up-power-bi-service-for-developing-a-visual, I kept getting an error "Can't contact visual server" per the following screenshot.
The issue turned out to be with the browser acknowledging the development certificate that is generated for localhost using pbiviz install-cert.
If you look at browser Dev Tools, you'll probably see an error "Failed to load resource" for localhost:8080/assets/status and if you navigate to this page, you'll get a message localhost refused to connect. ERR_CONNECTION_REFUSED.
I learnt that there is a setting in chromium based browsers (ie. Edge and Chrome) called #Allow invalid certificates for resources loaded from localhost.
You can get to this setting by navigating to edge://flags or chrome://flags and setting to enabled.
NOTE: I'd encourage you to research the possible security risks associated with changing this setting, but it should enable you to debug your visual.