After more than 30 emails with MailChimp here is a different response…
“Mady (MailChimp)
Jan 27, 1:25 PM EST
Hello Nahuel,
Thank you for reaching out to us. I understand your subscribers are not receiving a confirmation email.
I took a look at the account and it looks like the issue is with the way the signup form’s double opt-in is working with API calls.
We are currently aware of an issue with some double opt-in “pending” API calls not sending confirmation emails to subscribers and our developers have been notified. While we do not have an estimated time for this to be resolved by right now, it is being addressed and worked on.
Due to the Compliance state of the account, all subscribers added through API calls with a “pending” status will not be sent a confirmation email. A workaround you can try would be to switch to single opt-in API calls with a “subscribed” status. This should allow confirmation emails to be sent to subscribers.
If you are comfortable doing this yourself or if you have a developer who can do it for you, these API Docs will be helpful:
API Docs: https://developer.mailchimp.com/documentation/mailchimp/reference/overview/
The “status”: “pending” part of the calls will need to be something like “status”: “subscribed”.
If you do not have a developer and are looking for help, you can hire someone from our Experts Directory to help you with that:
Experts Directory: https://experts.mailchimp.com/
If you have any other questions, I would be happy to answer them for you. Have a nice day.
Thank You,
Mady”