Set-Cookie header not accepted by javascript fetch

Question

I've been trying for a couple of days now to set a cookie from my web server written in Go, and everything looks right but it just won't work.

My Set-Cookie header:

Set-Cookie: session_token=token; Path=/; Expires=Date; Max-Age=120000; HttpOnly; SameSite=Strict

I've tried editing all the values and removing and adding other fields but nothing helped. If I set my request to get and navigate directly to the link with browser cookie appears, and in Postman it is there, but when I try using fetch to get the http request it doesn't work. I know about credentials: "same-origin" and credentials: "include" but they don't work. Here is my js fetch code:

const log_in = (e) => {

 // data entry validation and stuff

 const url = "/signin";
  fetch(ip + url, {
    credentials: "same-origin",
    method: "POST",
    headers: {
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      username: document.getElementById("username").value,
      password: document.getElementById("password").value,
    }),
  }).then(
      () => console.log("recieved")
  );
};

Answer 1

This is not at all what I wanted but this is how I solved my problem if somebody is in the same boat as me... Using axios. I don't use node, yarn or whatever and using cdn gave me cors errors so I just copied the code from cdn file locally and that worked. You can se the code here:

axios({
      method: 'post',
      url: ip + url,
      data: {
        firstName: document.getElementById("username").value,
        lastName: document.getElementById("password").value
      },
      withCredentials: true
    })

I won't mark this as an answer since I wanted to do this with fetch and no 3rd party libraries but if this is someone's last resort this works...