When the site is running on the development way, "npm start", the backend url used is from the proxy at the package.json.
When i go for the production way "npm build", the backend url is not used from package.json, because that proxy is only for development.
I would like some help to understant how to configure that backend url, i am using the same url for both development and production.
In the configuration file .package.json:
{
  "name": "mysite_frontend_v1",
  "version": "0.1.0",
  "private": true,
  "proxy": "https://api.mysite.com",
...
} 
And then created a file .env :
REACT_APP_API_URI = 'https://api.mysite.com'
the api.js file :
function request(path, { data = null, token = null, method = 'GET' }) {
  return fetch(path, {
    method,
    headers: {
      Authorization: token ? `Token ${token}` : '',
      'Content-Type': 'application/json',
    },
    body: method !== 'GET' && method !== 'DELETE' ? JSON.stringify(data) : null,
  })
    .then((response) => {
      // If it is success
      if (response.ok) {
        if (method === 'DELETE') {
          // If delete, nothing return
          return true;
        }
        return response.json();
      }
      // Otherwise, if there are errors
      return response
        .json()
        .then((json) => {
          // Handle JSON error, response by the server
          if (response.status === 400) {
            const errors = Object.keys(json).map((k) => `${json[k].join(' ')}`);
            throw new Error(errors.join(' '));
          }
          throw new Error(JSON.stringify(json));
        })
        .catch((e) => {
          throw new Error(e);
        });
    })
    .catch((e) => {
      // Handle all errors
      toast(e.message, { type: 'error' });
    });
}
export function signIn(username, password) {
  return request('/auth/token/login/', {
    data: { username, password },
    method: 'POST',
  });
}
export function register(username, password) {
  return request('/auth/users/', {
    data: { username, password },
    method: 'POST',
  });
}
 
    