Opt in settings

i am trying to use mailchimp to harness my woocommerce email details when a customer checks out……

For those customers who check the “opt in” checkbox at checkout…
They are added to my Mailchimp “Audience”
However,
They are not a “Subscriber”,
Under the “email marketing” column, they are shown as blank,
when i click on the customers email, they are described as eligible for “Transactional emails only”

I would assume as they have checked the opt in box at checkout, they would be a subscriber?

Under the mail chimp settings (within wordpress), under “Audience settings”, the check box is described as follows:
“Opt-in Settings – Message for the opt-in checkbox – Add text to go along with the other opt-in checkboxes. – Customers can click a box at checkout to opt in to your newsletter”.

i would assume that any customer who selects the check box, is opting in to emails and would therefor be classed as a “subscriber”.

is this a bug? or functioning as expected and my expectations are not correct.

any help much appreciated.