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React native post-request with fetch is not working


New Coder
Hey I have a problem with my react native app.

I am very desperate, because I can't find a solution for more than a week.

I am sending data with react native and fetch to my express server. This is my fetch functionality:

fetch('', {
            method: 'POST',
            headers: {
                'Accept': 'application/json',
                'Content-Type': 'application/json',
            body: JSON.stringify({
                userName: userName,
                password: password,
            .then((response) => response.text)

My express server listens to this route:

app.post("/login", (req, res) => {
    console.log("Request: ", req.query)
    userRepository.login(req.query.userName, req.query.password)
        .then(() => {
            res.status(200).send("Login sucessfull")
        .catch(err => {
            res.status(401).send("" + err) //TODO Return as string or how is it supposed to be?

I tested to connect to the server with postman and I get response code 200 with the message "Login sucessfull"
But when I post it with my react native app, nothing happens. I logged the request and I get an empy object {} when I post with my app. When I post with postman, I get the login data I've sended
(And yes, I know, this isn't very secure to send login data. This is just for educational things. Encrypting and data security will be added after that)

What I thought would be, that I have to open the ports. I opened them, since my phone is another device than my laptop, which could explain, why postman can post and my app not. But it doesn't change anything. Actually I can connect with my smartphone to the server with a "get"-request over this route:

app.get("/", (req, res) => {
    res.send("Mainpage for faster debugging")

So the connection is not the problem. And since postman (and my phone-browser) can work it out, the server is also okay. So I think the problem is in my react native fetch function. Or did I have to set up something? I use the app on android.
Last edited by a moderator:

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