404 error when using Google App Engine with flask and flask-restplus

Your existing code only adds one blueprint, with the /api URL prefix, so it won't be able to handle requests for / or /favicon.ico (which many browsers request by default) - explaining the first 2 404 errors in your request log. If your app is intended to be visited by regular browsers you may want to add other blueprints to cover those URLs as well, otherwise those 404s are expected/normal.

I'm not familiar with flask and blueprints, so I'm unsure if the blueprint you have should, initiated as it presently is, serve already the /api/ URL. If not - that would explain the 3rd 404 in the request log. I suspect you may need to add a route/rule for it in the blueprint, tho.