Mailchimp API update existing member throws "Member already in list"

Question

I'm using the mailchimp marketing SDK for NodeJS

In the listed methods, there's a method called setListMember() which updates the member info if they are in the list, otherwise adds them. I've tried with several email addresses. One of them is causing the main issue.

• When I use a certain email address for updating the info using the same setListMember() method, it throws "Member already exists" error.
• If I only use updateListMember(), it throws same error.
• If I then try to add the member, who is already in the list, throws the same error.
• If I find the member in the list, it throws 404 Not found error.

All this issues happening with one particular email I found. Tried several potential fixes such as trimming, lowercase, white-space removing. None works. If anyone could help me out, I'd be grateful.