Mailchimp Block: Support double opt-in

[htdat]

Steps to reproduce

Currently, it's not possible to configure double opt-in with Mailchimp block.

1. Set up a list with double opt-in option in Mailchimp. My link to set it up looks like this https://us19.admin.mailchimp.com/lists/settings/defaults?id=xxxx
2. Set up this list with a Mailchimp block
3. Add an email to this list.
4. This email was added to the list without any double opt-in email.

What I expected

A double opt-in email.

What happened instead

This email was added to the list without any double opt-in email.

Context / Source

Tix: 2704143-zen

[kristarella]

I consider this a bug rather than a feature request since the double opt-in is a setting on the list/audience itself, not an aspect of the form.

+1 for this

11787946-hc

[stale]

This issue has been marked as stale. This happened because:

• It has been inactive in the past 6 months.
• It hasn’t been labeled `[Pri] Blocker`, `[Pri] High`.

No further action is needed. But it's worth checking if this ticket has clear reproduction steps and it is still reproducible. Feel free to close this issue if you think it's not valid anymore — if you do, please add a brief explanation.

[happychait]

A customer asked for it in 12275745-hc

[julsyd]

User request in 4959173-zen.

Info provided by Mailchimp:

There is an issue with the call we are receiving. We can see that contacts are sent as subscribers. They have to be sent as "pending" prob in order to trigger the double opt in. Here is the documentation on that: https://mailchimp.com/developer/marketing/api/list-members/

[jeherve]

Also in #32406