I’ve contact MC support and this is what they gave me:
Due to the GDPR requirements for EU, we recently added a new way to
delete contacts from your list. At this time, you can delete and
archive (which is a soft delete and keeps that contact in your
reports) or you can delete and remove (which is a hard delete and
removes those contacts from all reporting / etc). Seeing this error
message means you are trying to re-add someone that had been
previously permanently deleted. If you intend to delete someone and
re-add them via the API, you want to use the delete and archive
option.
The only confusing part for me was that I was asked to resubscribe when in fact it was the very thing I was doing, but the support team also told me that:
When seeing the message for ‘resubscribe’, this is referring to using
a MailChimp signup form as opposed to using an API subscribe method.
The MailChimp forms are the ultimate ‘workaround’ in which it can be
used to resubscribe unsubscribers, cleaned addresses or permanently
deleted addresses.
In summary, there is nothing wrong the code it’s just how MC treats that request from their API which I believe shouldn’t be as misleading as the error message says.
So there you go, I hope this helps someone who’s been in the same painful path of discovering that there’s nothing wrong with your code and that was just simply how their API worked. ¯_(ツ)_/¯