Based on my quick look at the code

includes/functions/extra_functions/mailchimp_functions.php Line 8

Code:

Code:
'status' => 'pending'
change to

Code:

Code:
'status' => 'subscribed'

From Mailchimp API docs
Subscriber Status

To add a subscriber, you must include the subscriber’s status in your JSON object.

Use subscribed to add an address right away.
Use pending to send a confirmation email.
Use unsubscribed or cleaned to archive unused addresses.

The unsubscribed option is useful if you import addresses from another service. When you add subscribers to the unsubscribed or cleaned status groups, you’ll have a record of the subscriber, and we’ll prevent sends to that address in the future. That’s ideal for inactive or unsubscribed addresses, which can increase spam complaints if they’re accidentally added as subscribed.