could not proxy request /api/customers

[nwheatleKite]

This was working for me a few days ago (I think?). However, today I cloned this repository, ran npm install for both server and client, and then ran the app with npm run dev.

The proxy is not working. No customers are fetched.

This is the terminal output:
[0] > nodemon server.js
[0]
[0] [nodemon] 1.19.1
[0] [nodemon] to restart at any time, enter rs
[0] [nodemon] watching: .
[0] [nodemon] starting node server.js
[1]
[1] > client@0.1.0 start C:\Users\nwheatley\Documents\DockerApps\fuck\react_redux_express_starter\client
[1] > react-scripts start
[1]
[1] Starting the development server...
[1]
[1] Browserslist: caniuse-lite is outdated. Please run next command npm update
[1] Compiled successfully!
[1]
[1] You can now view client in the browser.
[1]
[1] Local: http://localhost:3000/
[1] On Your Network: http://192.168.2.170:3000/
[1]
[1] Note that the development build is not optimized.
[1] To create a production build, use npm run build.
[1]
[1] Proxy error: Could not proxy request /api/customers from localhost:3000 to http://localhost:5000/.
[1] See https://nodejs.org/api/errors.html#errors_common_system_errors for more information (ECONNRESET).
[1]
[1] Proxy error: Could not proxy request /sockjs-node/346/4ps1wehg/websocket from localhost:3000 to http://localhost:5000/.
[1] See https://nodejs.org/api/errors.html#errors_common_system_errors for more information (ECONNRESET).

I even tried adding proxy http middleware - and it still is stuck on client port 3000.

const { createProxyMiddleware } = require("http-proxy-middleware");

How can this be fixed?

OS Windows 10 Enterprise
Version 1809