title: Expected a valid shop query parameter
body: <p>I'm trying to create new Shopify app using shopify-app-cli, I set up all redirect links and .env file, but when I run Shopify serve and when it says Ready on <a href="http://localhost:8081" rel="nofollow noreferrer">http://localhost:8081</a>, I go to localhost page and it shows this error: Expected a valid shop query parameter.
  What does it mean?</p>
  
  <p>I checked my .env file for maybe typos, but everything is copied fine.</p>