New user, trying to get basic setup working

Hi all.

I'm trying to learn traefik and having some difficulties.

I have traefik running on server A (192.168.1.2) and want to proxy requests for /nr to a node-red server running on server B (192.168.1.10)

However, no matter how I try to configure it, when I point my browser to 192.168.1.2/nr I get a 404.

Here is my config.yaml

entryPoints:
web:
address: ":80"
providers:
file:
filename: ./test.yaml
log:
filePath: "./log.txt"
format: json
level: DEBUG

Like I said, pretty simple.

Here is the test.yaml file:

http:
routers:
nodered:
rule: "PathPrefix(/nr)"
service: node-red
services:
node-red:
loadBalancer:
servers:
- url: "http://192.168.1.10:1880/"

So, what am I doing wrong? Once I get this working, I can start adding other endpoints and eventually, TLS via let's encrypt.

Thanks in advance,

Mike.