Module fails to update MailChimp ECommerce360 conversion information after sales

I'm hoping someone can shed some light on why no orders are showing up in my Mailchimp account in terms of e-commerce 360 tracking.

- I've created a campaign and enabled 'ecommerce 360 tracking' in that obscure little dropdown on pane 2.
- the latest versions of ubercart, drupal mailchimp, and uc_mailchimp are installed.
- i link directly to an ubercart node in the email
- cookies called 'mailchimp_campaign_id' and 'mailchimp_email_id' are created in the browser after following the links
- i've got debug mode turned on, but nothing shows up in the logs.
- i've tried without debug mode on too.
- the eCommerce function is in the right place in my conditional actions, and all the other things in that group happen.
- my mailchimp id/password are correct, and new customers do get added to the specified mailing list.
- i do get output that looks like this when I purchase as the administrator, but that's the only sign of anything:

Array
(
    [0] => ac7289d18c
    [1] => email@example.com
    [2] => Array
        (
            [FNAME] => 
            [LNAME] => 
        )

    [3] => html
    [4] => 
    [5] => 1
)

I've completed several different types of transactions, some using the 'free payment method' module, and some transactions for $5-$10 that have gone through the paypal sandbox system, but nothing ever shows up in my Mailchimp campaign reports. Not even a eCommerce 360 box that says 'no data received' like it does for Google Analytics 360. I imagine if it were working correctly there would be another similar box that had order info by list member?

One thought I've had is that maybe since I'm not collecting FNAME and LNAME information, something is choking along the way due to empty fields?

Or is it dependent on the actual live paypal system instead of the sandbox servers?

Anyway, just hoping for a pointer in the right direction or a way to test where in the chain things are breaking down.

Thanks,

(c)