I am sending POST request like this from browser:

fetch(serverEndpoint, {

    method: 'POST',

    mode: 'no-cors', // this is to prevent browser from sending 'OPTIONS' method request first

    redirect: 'follow',

    headers: new Headers({

            'Content-Type': 'text/plain',

            'X-My-Custom-Header': 'value-v',

            'Authorization': 'Bearer ' + token,

    }),

    body: companyName

})

By the time the request reaches my back-end it does not contain X-My-Custom-Header nor Authorization header.

My back-end is Google Cloud function for Firebase (basically just Node.js endpoint) that looks like this:

exports.createCompany = functions.https.onRequest((req, res) => {

    let headers = ['Headers: ']

    for (let header in req.headers) {

        headers.push(`${header} : ${req.headers[header]}`)

    }

    console.log(headers)

    ...

}

The console log of that Google Cloud for Firebase function does not contain any X-My-Custom-Header nor Authorization header.

What is wrong?

Edit 1

So using dev tools in Chrome a checked that neither X-My-Custom-Header nor Authorization header is send from the browser... The questions now are: Why? How do I fix it?

Edit 2

More information about my app: It's React app. I have disabled service worker. I have tried to create Request and specifically add headers using req.headers.append(). The headers still wouldn't send.