var formdata = new FormData();
formdata.append("name", "John Smith");
formdata.append("email", "test@test.net");
formdata.append("phone", "+14091453225");
formdata.append("address", "Pasadena, Lower Peters Canyon, Irvine, Orange County, USA");
formdata.append("geolocation", ""); // То, что возвращает сервис https://locationiq.com, в виде json-строки

var requestOptions = {
  method: 'POST',
  body: formdata,
  redirect: 'follow'
};

fetch("https://beta-api.solo-crm.com/mc/form", requestOptions)
  .then(response => response.text())
  .then(result => console.log(result))
  .catch(error => console.log('error', error));