Why my fetch request have problem Network Request Error in react native

Question

I have written this code but I always get a network request failed error.

const res = await fetch('https://mydomain:8099/login', {
    method: 'POST',
    headers: {
        'Accept': '*/*',
        'Content-Type': 'application/json',
        "Access-Control-Allow-Origin": "*",
    },
    body: JSON.stringify({
        user: "my user name",
        password: "my password"
    })
});
console.log(res);
return res;