Why do post requests fail, but GET requests do?

Question

Nginx

Probably a boring question, but I'm at an impasse.
There is a remote test server on debian, NGINX is configured on it, which proxies the necessary requests to the local node express server service (not docker).
One server on localhost:3001 to work with the database, everything is fine here, all REST requests go through (POST, GET ....).
And the second one on localhost:3002 for uploading images. Here I have a problem with CORS
Error in the browser (Local page on VUE (npm run serve) with axios requests)

Access to XMLHttpRequest at ' https://myTestServer/uploadImg ' from origin ' localhost:8080 ' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: Redirect is not allowed for a preflight request.

I already tried everything in express:

app.use(function (req, res, next) {
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
    res.header('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, OPTIONS');
    next();
});

And I used the module https://www.npmjs.com/package/cors
app.use(cors())
It doesn't help... :(
It's interesting that there are no problems on the localhost:3001 service with the same cors settings. I
also see the first request in the NGIX logs when trying to download images through the browser OPTIONS

"OPTIONS /uploadImg HTTP/1.1" 301 169 "http://localhost:8080/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36" "-"

What could be the problem ?
PS tests with POSTMAN pass successfully, as well as GET (if you just open the page in the browser)

Answer 1

Found the problem.
From the client, I sent requests to

' https://myTestServer/uploadImg ' 

so I get an error
But if I send a request with a slash at the end

https://mytestserver/uploadimg/

this is how it works
Although on the server

app.post('/uploadImg', async(req, res) => {

Perhaps because in nginx

location /uploadimg/

although it is strange, since the first service with requests without a slash at the end works ... files are not accepted there

Answer 2

In Access-Control-Allow-Headers try adding Redirect.