Google Form Apps Script to create new subscriber in MailChimp via API including GDPR opt-in

GoogleForm-AppsScript-MailChimp-API-GDPR-Code.gs

// make sure you have added an event trigger for OnFormSubmit to run the onFormSubmit() function or this won't even run

var APIKEY = "1234567890abcdef1234567890abcdef-us11"; // your MailChimp API key
var LISTID = "ababababab"; // hint: not an integer
var GDPRID = "cdcdcdcdcd"; // hint: this seems to be unique per list, so you'll have to find this yourself
var FORMSHEETNAME = "Form Responses 1"; // your Google Sheets target sheet name (this is the likely name if you didn't change it)
var EMAILCOLUMN = 6; // the column number (1=first) that contains the email field name
var XTRAPARTCOLUMN = 5; // the column number (1=first) that contains the field name for whatever you want this field to be
var XTRAPARTNAME = "XTRAPART"; // the merge field name of the extra field you're storing in (you have to make this yourself; it's here as an example of how you might populate a custom field)

var BASEURL = "https://"+APIKEY.match(/-(.+)$/)[1]+".api.mailchimp.com/3.0";
var FORMSHEET = SpreadsheetApp.getActive().getSheetByName(FORMSHEETNAME);
var EMAILFIELDNAME = FORMSHEET.getRange(1, EMAILCOLUMN).getValue();
var XTRAPARTFIELDNAME = FORMSHEET.getRange(1, XTRAPARTCOLUMN).getValue();

function addSubscriber(email, xtrapart) {
  if (!email) return;
  var url = BASEURL+"/lists/"+LISTID+"/members";
  var merge_fields = {};
  merge_fields[XTRAPARTNAME] = xtrapart || "";
  var result = UrlFetchApp.fetch(url, {
    muteHttpExceptions: true,
    headers: {"Authorization": "Basic " + Utilities.base64Encode(LISTID+":"+APIKEY)},
    method: "post",
    contentType: "application/json; charset=utf-8",
    payload: JSON.stringify({
      email_address: email,
      status: "subscribed",
      merge_fields: merge_fields,
      marketing_permissions: [{
        marketing_permission_id: GDPRID, // GDPR Email Opt-in
        enabled: true,
      }],
    }),
  });
  Logger.log(result);
}

function onFormSubmit(e) {
  Logger.log(e.namedValues);
  var email = e.namedValues[EMAILFIELDNAME] ? e.namedValues[EMAILFIELDNAME][0] : "";
  var xtrapart = e.namedValues[XTRAPARTFIELDNAME] ? e.namedValues[XTRAPARTFIELDNAME][0] : "";
  if (!email) return;
  addSubscriber(email, xtrapart);
}