As of 2 April 2019 MailChimp shut off V1.3 API support which is the API that S2Member uses to connect to MailChimp.
So S2Member MailChimp list-server functionality (see https://s2member.com/kb-article/integrating-mailchimp/ ) won’t work again until someone re-writes the MailChimp S2Member code.
Just a heads-up everyone.
I cannot confirm that: I haven’t noticed a problem with MC integration yet.
And we do use ALL allowed 30 custom fields in MC, and so far site/MC data transmits nicely it seems.
Of course email subscriptions work too.
Maybe the impact isn’t as big as you think?
Cheers David. That is indeed puzzling. I enabled MailChimp registration field for a client a few days ago and it failed to operate. The S2Member logfile had some weird crash data that included a lot of plaintext CSS. That’s when I checked and found that MailChimp has turned off the API (as per supplied link). I was planning on forking the S2Member non-pro software and adding in up-to-date MailChimp software over the next few months.
I’m certainly happy for you that it is still working…though I’m puzzled as to why the discrepency with the MailChimp announcement. I checked the S2Member source code and they are, indeed, using the deprecated V1.3 API.
You’re sure you don’t have another MailChimp plugin installed and in use?
I quickly looked for you: the only plugin I can think of that might quietly have an api is blog2social?
I guess i can be so confident because our MC signup is handcoded, no plugin (MC’s own WP plugin had shitty reviews at the time)
Basically THIS GREAT NEW BOSS CRISTIAN 
was the one who helped, I remember.
He pointed me to some stuff about must-use plugin and code that I as non-coder didn’t understand but was able to copy
Cristian for President!
REAL president I mean. Not that 2yr old JOKE able to sway some citizens into BELIEVERS like a rural church priest on a rainy Sunday…
Cheers for the update David. I’ll try to sort out the contradiction between:
It’s a mystery for sure…I’ll dig into it late next week when I have some available time and update this post
Thank you for the heads up, Tim.
I found MailChimp’s announcement. https://mailchi.mp/195471f5dad4/important-information-about-your-integration-219125
They say they emailed those using the old APi, I didn’t get that email, and no user has told me about getting this warning sooner. I found a guy mention having gotten this back in February: http://lasso.2283332.n4.nabble.com/Mailchimp-will-shut-down-API-1-1-1-2-and-1-3-on-April-2-2019-td4646643.html
Anyway, I’m studying what this needs to get it sorted out and the integration working. I’m very sorry about the inconvenience.
Cheers Cristian. Certainly no apology necessary from you
I took a look at the software. There is a fair bit of it so getting a handle on it and knowing what to update won’t be a trivial task. The bulk of the software is external, written by someone else, and has not been updated by the external party since 2015 (https://github.com/alleyinteractive/mailchimp-ajax/tree/master/mailchimp-api/src/Mailchimp ). The author did not put copyright statements in the software so it took some creative Google searching to track it down.
The previous S2Member team raised a MailChimp issue to update the MailChimp API in 2016 but it was never actioned (https://github.com/wpsharks/s2member/issues/999).
Let me know if you can commit to a scheduled update. If not, I will likely fork S2Member (non-pro) and update the MailChimp next month. You can reverse port it back from my fork if you don’t get around to doing your own update during that time.
I can’t commit to a date, but I will work on this as a high priority as much as can. When I have something ready, I’ll post an update here. Feel free to fork the repo and do with it what you need to. I hope to have something for you before you have to spend time on it, though. 
That would be great
NOTE: It is not my intention to compete with S2Member (I’m pleased that you are rejuvenating it) but in the absence of a planned release schedule I will need to fork and update for my clients. Since you will have your priority schedule and I will have mine I expect forking and running in parallel and reverse porting where one stream updates ahead of the other might be an effective way forward.
Sure, no problem at all, it’s open source. Send a pull request whenever you feel like it, too.
What are your priorities to take care of? Just curious to know what the overlap with my list is.
Updates in order of priority:
I think S2Member had the right balance when it was first launched but then got stretched by the payment obligations. If I look at the forum a lot of issues are payments related. Trying to keep up with payment challenges is a full-time job.
Tell me about it… lol
And I want to add more gateways while reducing the load… I have some ideas in mind, we’ll see.
Many items of your list are on mine too.
What do you mean by groups? BuddyPress? And P5.x?
Protected content groups.
The S2Member is level-based which is powerful in one respect but limiting in another.
I have client scenarios where they want to protect content by user group.
There are various ways to accomplish this using S2Member (e.g. add a capability to all the content and assign it to appropriate users, or create a custom role and protect by role, etc) but none are intuitive and can end up requiring custom code or manual effort to maintain.
What would be useful is a UI that allows the selection of content that belongs to a group and a UI that allows the association between users and content groups.
This is not meant to replace the current S2Member model…just augments it.
Got it. Thanks for the description.
I was studying the new API and studying s2Member’s current implementation to see what was needed, and noticed that s2Member shouldn’t be affected by what was announced by MailChimp.
The announcement said that they “decided to shut down Mailchimp API 1.1, 1.2, and 1.3, and now require that all integrations be on 2.0 or higher, and preferably 3.0”.
s2Member uses version 2 of their API: /src/includes/externals/mailchimp/Mailchimp.php
public $root = 'https://api.mailchimp.com/2.0';
So, that’s a relief.