title: Slack slash command with local web service
body: <p>I put a local web service (started with 10.xx) in the <code>Request URL</code> section of a Slack slash command setting.
  When invoking in the channel, it gives me <code>503_service_error</code>.</p>
  
  <p>Our company is using Slack, and I'm in one of its workspaces, Is there any workaround that this workspace can access a private IP.</p>
  
  <p>PS: the URL I configured is accessible from my desktop.</p>