Why is the web browser not setting my cookie?

Question

I am using the cookie-session package.

app.use(
  cookieSession({ 
    signed: false, 
    secure: false 
  })
);

When a user signs up, I set the session property to an object.

req.session = { jwt: userJwt };

The cookie is successfully sent to the browser, as seen in Response Cookies.

The browser does NOT set the cookie.

My frontend runs on http://localhost:1234 and my server runs on http://localhost:3000.

I am NOT currently proxying requests in development i.e. to sign up I hit http://localhost:3000/api/users/signup.