When making this request:
// Subscribe a new account holder to a MailChimp list
function subscribeSomeoneToMailChimpList()
{
var options =
{
\"apikey\":
After further research & tinkering, I was able to solve this:
https://.api.mailchimp.com/2.0/lists/subscribe.json?apikey=&id=&email[email]=test@test.com&merge_vars[FNAME]=John&merge_vars[LNAME]=Doe&double_optin=false&send_welcome=false
Where
should be replaced with the portion after the dash in your API Key. e.g. "us1", "us2", "uk1", etc.