

First party sites are how my credit card gets leaked every single time. The incompetence is thorough at every level.
My personal trick is even in my own country to get new travel credit cards regularly. The first one I got was scammed on my first booking. I alerted the hotel and they said it couldn’t possibly be them. They’re the only company that ever got those details it can only be them.
404 is a web server response suggesting that a web server is up. It’s what’s giving 404.
The web server can’t find your page or document or resource. So one of your web servers (on either the reverse proxy or the actual server) is pointing to the wrong spot on what to serve.
You haven’t tried launching a wrong server on the same port right? Or misconfigured your nginx translation?
Isolate the issue. Ignore nginx and start testing just the web server on the destination and see if the server is giving 404 and then if it is giving the right document then it’s nginx configuration. If it’s not giving you the document nginx can’t serve.
But either way start isolating the problem into the smallest area. And focus on the configurations and files that are related to it.