Mailpoet Custom Forms and Custom Fields

I've created a custom mailpoet form and am trying to add subscribers through it. It works when I don't try to post custom form field data. Does anyone know how I can make it work with custom form fields? In the database it has cf_1, cf_2 etc and this is what I've tried amending the code here without much luck: http://ift.tt/1W5JRV9

$user_data = array(
    'email' => $email,
    'firstname' => $firstname,
    'lastname' => $lastname,
    'cf_1' => $phone,
    'cf_2' => $company_name,
    'cf_3' => $dob,
);

Any ideas? Cheers!

via Chebli Mohamed