What operating system are you on? Is anything else running on :3000? Are you using Trellis? Have you followed our Getting Started documentation to make sure your environment is set up correctly?
Does http://example.test load the site for you? If not, that’s something unrelated to Sage since you already need a working local dev setup/webserver in order to use the build process
Does http://example.test load the site for you? If not, that’s something unrelated to Sage since you already need a working local dev setup/webserver in order to use the build process