title: Google app engine and axios post request
body: <p>I have app engine web service deployed. I have suddenly found, once clicked service name (default) link in services section of app engine, it redirects me from <a href="https://myapp-api.appspot.com/" rel="nofollow noreferrer">https://myapp-api.appspot.com/</a> to <a href="https://version-1-dot-myapp-api.appspot-preview.com/" rel="nofollow noreferrer">https://version-1-dot-myapp-api.appspot-preview.com/</a>.</p>
  
  <p>Having client application using axios node js lib (running on http), i found it giving errors trying to do POST request from client (http) to myapp (https). My app does support accepting ajax calls setting Allow-Control-Allow-Origin header. GET requests work fine. </p>
  
  <p>POST request gives: UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 8): Error: Request failed with status code 400</p>
  
  <p>If i replace API url from the original one to <a href="https://version-1-dot-myapp-api.appspot-preview.com/" rel="nofollow noreferrer">https://version-1-dot-myapp-api.appspot-preview.com/</a>, it works. </p>
  
  <p>Any idea why? What am i doing wrong? Should i permanently replace URL to preview one? Why POST request for short URL throws an exception? </p>