If it's failing on both the https://host:port/new_post and the https://host:port/ endpoints then it looks like some sort of issue with Flask or Python requests.
It might be related to your use of SSL but if Apache's handling it, then I'm not too sure what would be causing the issue. Are you able to temporarily disable SSL and test out the integration, for troubleshooting purposes?
I also checked the requirements.txt to see if it has the latest versions of Flask and Python Requests. Flask is latest at 0.10.1 but Requests is at 2.2.1 when the latest is 2.8.1. So you can try upgrading Requests to the latest version with pip install requests==2.8.1.