Axios - Basic Auth not working

I have to do a POST login request in an API, however I have a problem requesting with the axios.

I set up the request following the documentation of the own axios, using 'auth' in the creation of the 'axios instance', see:

  const instance = axios.create({
    headers: {
      'Content-Type': 'application/json'
    },
    auth: {
      username: 'username', //A senha obviamente não é essa, porém esotu usando as credenciais corretas pois testo no Postman e funciona.
      password: 'senha'
    }
  });

The request:

const request=instance.post('${config.UNIMED_API.development}/wsunimedpj/login', payload);

But the request does not even get done, when I analyze the traffic through the network of the browser is the response:

HTTP Status 401: Full authentication is required to access this resource

What am I forgetting / doing wrong?

Thank you!