TOPIC: 400: is already a list member. Use PUT to...

I'm getting a signup message "400: is already a list member. Use PUT to insert or update list members."

I had a report from a client that the signup wasn't working so updated everything tested via business email. This email was originally in the mailchimp list, I manually deleted it from client's mailchimp accont. Have synced several times. It appears that once signed up and manually removed the user cannot signup again via the website?
New signups are still working fine.

Joomla 3.6.2 & CMC 3.0.0
Many thanks

Hey Phil,
Have you ocnfigured the webhooks url? I've seen something similar. The problem is that once you sign up once - your are not subscribed for the list until you hit the link in the mail. But if you want to subscribe a second time through the module - mailchimp doesn't tell us that the user is on the list and when we try to insert him again - we get that error.

Regards,
Daniel

No, wait. I found that our check if the user is already on the list doesn't check for anything else than "subscribed" so even if the API returns pending, we treat the user as not on the list and try to create it instead of updating it. It will be fixed with 3.0.1 later today.

Super thanks for your input and time, it is appreciated.