Trouble adding new users

Hi all,

My knowledge of PHP is pretty limited, so I’m having trouble resolving this problem.

With every new order that we’ve tested and opt-in for the newsletter, we’re receiving this message in our mailbox:

SS_WC_MailChimp_Handler::subscribe(): WooCommerce MailChimp subscription failed: Your merge fields were invalid. (ss-wc-mc-api-request-error)

What are we doing wrong? I don’t really see any way to fix this on Woocommerce Mailchimp’s settings page.

Any help is much appreciated!