I have searched around, but still can't get it to work. I followed this blog to set things up.

this is where I send my cookie (server):

//after user is has been authenticated
export const logInUser = async (req, res, next) => {
try {
  const token = getToken({ _id: req.user._id, username: req.user.username, email: req.user.email})
  const refreshToken = getRefreshToken({  _id: req.user._id, username: req.user.username, email: req.user.email})
  await User.findOne({ username: req.user.username}).then((user)=>{
      user.refreshToken.push({ refreshToken })
      user.save((error, user) => {
        if (error) {
          res.status(500).json(error)
        } else {
          //sending the cookie
          res.cookie("refreshToken", refreshToken, {httpOnly: true, secure: !dev, signed: true, maxAge: (60 * 60 * 24 * 30) * 1000, sameSite: "none"})
          res.send({ success: true, token,  _id: req.user._id, username: req.user.username, email: req.user.email})
        }
      })
    })
} catch (error) {
  next(error)
    res.status(500).json(error)
    console.log(error)
}
}

index.js (server):

const corsOptions ={
origin: true, 
credentials:true,
optionSuccessStatus:200
}
app.use(express.json());
app.use(helmet());
app.use(morgan("common"));
app.use(cookieParser(process.env.COOKIE_SECRET))
app.use(cors(corsOptions));
app.use(passport.initialize());

making the request on the client-side (using next.js):

function login(username, password) {
axios.post("http://localhost:5000/api/auth/login", {username, password}, {withCredentials: true, credentials: 'include'}).then((res)=>{
  setCurrentUser(res.data)
}).catch((error)=>{
  console.log(error)
})
}

Response in browser

Everything works perfectly in postman