Request failed, status code 404 with POST requests

I’m new to Netlify
I have this routing on expressjs (server.js) which allows me to upload a file received from axios (formData).
It works fine on local and saves it to the selected directory (directory /w which is a child of my publish directory). The server uses multer to work out the diskStorage, filename and the directory, which is " cb(null, ‘/w’) ".
On the client side, here is the Axios POST request in the publish directory.“”, formdata, {})

It throws an error “Request failed with status code 404” but works fine on local.

I’m a bit confused…
is it due to redirecting? cause if it is, I have made a _redirects file with

/upload /upload 200!

inside it
Is it because I need large media? Because that’s activated too…

Why would uploading work perfectly on local and not here? Cors issues? wrong directory?
I’m sorry for my ignorance, I need help.

EDIT: I have modified the server side’s routing function and it looks like it’s a routing / redirecting problem. I set it so that express would send a simple string if I go to /upload:’/upload’,function(req, res) {
return res.send(" Testing if this works : yup this is an empty page");

However I get “page not found”.
So now I don’t know what to do…

Thank you

Ok I found this:

Seems like relying on expressJS is not going to work

that’s correct, @BenL. Let me know if you have additional questions.