var response = await dio.post('https://campaigns.zoho.com/api/v1.1/json/listsubscribe',
    options: Options(headers: {
          "Content-Type": "text/plain",
          "Authorization": "Bearer 1000.46ac602dd00b439dc31b0c29598058a8.******455495f88892b24"
    }),
  data: {
  "listkey": "3z364b65e2a05e8aea080b39b2b3**********************",
  "contactinfo": {"First Name":"William","Last Name":"Last","Contact Email":"myemail@gmail.com"}
});