Issue deploying dash-flask app with ShinyProxy

I am recently developing a python dash app using flask as the embedding server, which can route to a path using render_template to render a html webpage generated within dash. It works well on my local windows machine and on AWS EC2 instance. However, when I deploy this app with shinyproxy, the dash UI part can appear, but it just cannot route the html webpage.(e.g. I cannot download the generated html webpage) Instead, the browser says 404 NOT FOUND. Anyone has experience deploying dash-flask app with ShinyProxy? Any help will be appreciated!