Nginx "Cannot GET /index.html" on proxy_pass to working domain - node.js

Question

Let me jump right in to it: I'm trying to proxy_pass my base URL (test.co) to another domain (webflow.test.co). But, to put it simply, I'm having trouble. I've solved a lot of the issues so far, but am stuck here again. The domain (webflow.test.co) is working fine, so no issues there... but when I try to use the proxy_pass (shown below) i get an error in-browser of "Cannot GET /index.html".
A look at Chrome Dev Tools shows that the redirect to webflow.test.co isn't happening (I think, I'm no expert with this area of the devtools) and maybe isn't able to retrieve index.html for that reason.
Here's my nginx config file (I'm routing all requests other than the home to my NodeJS server):
upstream nodejs {
server 127.0.0.1:8081;
keepalive 256;
}
# Redirect all non-HTTPS to non-WWW HTTPS
server {
listen 8080;
server_name "~^(?:www\.)?(.*)$";
return 301 https://$host$request_uri;
}
# Redirect WWW HTTP to non-WWW HTTP
server {
listen 4430;
server_name "~^www\.(.*)$";
return 301 https://$1$request_uri;
}
server {
location / {
proxy_pass https://webflow.test.co;
proxy_set_header Connection "";
proxy_http_version 1.1;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto https;
}
}
# Reverse-proxy to http://nodejs
server {
listen 4430;
server_name "~^(?!www\.).*$";
client_max_body_size 50M;
location ~ /(?<all>.+) {
proxy_pass http://nodejs;
proxy_set_header Connection "";
proxy_http_version 1.1;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
Any help is greatly, greatly appreciated. I'll accept the first answer that works and is sensible. Thanks so much!
EDIT 1: I just tested without using SSL at all, and the response is the same - Cannot GET /index.html, while the actual domain webflow.test.co works fine.