Connect to remote Express API from Postman - express

Question

I am trying to connect to my API, hosted on a remote VPS, via Postman but can't seem to find any definitive guides on how to do it.
The VPS has a frontend app (Vue) that connects to Express using Nginx reverse proxy. That works fine.
However, I want to share some of the Express API with another client not hosted on the same server. For example, connecting from Postman with user authentication to just share data in JSON format.
If anyone can give me any advice on how to achieve this I would much appreciate it.
EDIT
Here is an example request I am trying from Postman. Express is confirmed running on 3001 on the VPS.
http://vps-url:3001/test
This is the corresponding route in Express
app.get("/test", (req,res)=>{
res.json({ msg: 'Hello from VPS!' })
})
When I try to access in Postman, is just hangs.
I have also this CORS config to allow connection from my local machine using my public IP.
app.use((req, res, next) => {
const corsWhitelist = [
'http://vps-url.com',
'https://anotherclient',
'70.80.xxx.xxx' // my machine IP
];
if (corsWhitelist.indexOf(req.headers.origin) !== -1) {
res.header('Access-Control-Allow-Origin', req.headers.origin);
res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept');
}
next();
});