Implicit Registration not working

I’m running a buddypress site: carebox.community
I’ve set up a mailchimp account and generated an API
Installed the Mailchimp for wordpress plugin and gone through the buddypress settings for integration as follows:

Enabled? Yes
Implicit? Yes
Mailchimp Lists – my mailchimp list
Double Op-in? No
Update existing subscribers? Yes
Replace Interest Groups? No

I’ve done a few test signups to the site which have been successful, but the new members have not been added to the mailchimp list. I’ve tried both Yes and No on the double opt-in and got zero results in getting new registrations into my mailchimp list.

I think switched the Implicit option to no and a checkbox appeared on the registration form – if I go down this route new members to the site are added to the mailchimp list. I don’t want to use this option though and want to go down the Implicit route.

Any idea why this isn’t working?