First thing that I would do in this approach would be to try accessing the resource from the machine locally—so can you try that first and let me know if you can access it locally?

403 basically means that the web server is not allowing you to access the resource, it might come from a bunch of several reasons, such as having a server-able file (.html) in the directory and allowing your folder to be accessed from public internet.

Check out these resources to follow up on this topic, https://www.digitalocean.com/community/questions/nginx-403-forbidden–2, it also contains another article that might be able to help you troubleshoot this problem.