How to show Mailchimp opt-in box on third party registration form

I want new users who sign up to be automatically added to my mailchimp list. I have the mailchimp listserv parameters correcly configured in S2member - as a test, the optin checkbox appears in both the default wordpress registration form (/login?action=register) and in the S2member Pro registration form.

However I’m using a third party registration form which looks better as a popup. But for some reason the optin box is not showing in the form, and as a result new users are not auto subscribed to the mailchimp list. I tried manually adding HTML for the optin checkbox to the 3d party form (copied from the default wordpress form), but no cigar.

Any suggestions ?

Thanks

Try this plugin, but I think you may need to create your own form and pop-up page.

Thanks but this does not help, it does not do what I need

Then ask the creator of the “third party registration form” to make it to works by WP standards, and s2M will recognize new users - s2M is fully WP compliant.

Thanks Krum, S2M does recognize new users that sign up through the third party form, only problem is the new users are not auto enrolled in the Mailchimp listserv because the optin box does not appear on the form.

Well, then the only way is to synchronize them with the plugin I gave, the Pro version can do that.