First install http-server and ngrok globally
npm i -g http-server ngrok
Run a local web server
http-server -p 8080
Create a publicly facing URI to connect to you local web server
ngrok http 8080
Browse to
https://<your sub domain>.ngrok.io/atlassian-connect.json
to make sure the app is running.
Open up the app in your editor and open your atlassian-connect.json file. Find the baseUrl property and change it to
https://<your sub domain>.ngrok.io
Navigate to the “Manage add-ons” section in Confluence.
Click the “Upload add-on” link and paste in the url to you atlassian-connect.json file
https://<your sub domain>.ngrok.io/atlassian-connect.json
Then hit “upload”.