Serve Flask-Restplus API

I have a flask-restplus api that I built with Gunicorn, Nginx, and docker support. It works well in this setup.
I recently discovered Kong, and I would like to serve my API using Kong. I have already setup everything with docker. I added my service and routes. The API works fine.

I have a problem displaying the API documentation though. I tried to create a route as “/api” which corresponds to “my_api_address/api” where the swagger documentation is served. I can see that the request is being redirected to the upstream, however, it shows me “swagger.json” 404 not found (please see picture).

Would you please suggest how to fix this issue?