Have you registered a service with alias 'quotes' in admin console --> Add-ons --> App Services ??
There was a typo, the alias is connector1. I have updated the image in my post.
I have setup my App Service as
Service URL: http://XXXXXXX.azurewebsites.net (web api root URL)
Am I missing something?
It seems like there were some caching issue. I uninstalled the app and uploaded the zip file again and now the error is gone.