mailchimp.js

function b64EncodeUnicode(str) {
  return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g,
    function toSolidBytes(match, p1) {
      return String.fromCharCode('0x' + p1);
    }));
}

fetch('https://us17.api.mailchimp.com/3.0/lists/185415c92c/members', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'Authorization': `Basic ${b64EncodeUnicode('silencerweb:8ec49e64f2041073d3fe56e0abc5fe5f-us17')}`,
  },
  body: JSON.stringify({
    email_address: 'email@mail.ru',
    status: 'subscribed',
  }),
  mode: 'no-cors',
})