Random 'werkzeug.routing.BuildError' when testing Flask-Restful application
You need to assign events_items inside the 'fields.Url' before returning it.
This link How to add fields url for nested output fields in flask restful explains more
But if you are using Blueprints, add "." to the fields.Url eg 'uri': fields.Url('.events_items')
ref https://github.com/flask-restful/flask-restful/issues/266#issuecomment-46678118