MailChimp API PUT update list member

Question

Starting January 16, 2024 this endpoint seems to have broke.

Add or update a list member.

https://mailchimp.com/developer/marketing/api/list-members/add-or-update-list-member/.
PUT /lists/{list_id}/members/{subscriber_hash}

I can still add new members from this endpoint, but updating returns this error:

{
    "title": "Member Exists",
    "status": 400,
    "detail": "***@******.com is already a list member. Use PUT to insert or update list members.",
    "instance": "a808bd33-ddcf-5658-3e4a-601fe33616b7"
}

I've contact support, but they are useless and just send me docs for the API. Any hack or trick to get this to work again?

Answer 1

Turned out to be an issue with a single email address. I removed that email address, re-subscribed it and now the endpoint works as expected.