Custom integration do not work

I trying to add subscription checkbox to the popup form.
It is simple HTML form generated from Salesforce (if it is important).

I set up custom integration in plugin settings according to instruction and added custom field to the form.

Plugin is associated with Mailchimp. And I cand some subscriber were added via CF7 integration.

But for some reason it does not work for custom integration.
Can you please help me to make it work?

<input type="checkbox" name="mc4wp-subscribe" value="1" /> Sign me up for the newsletter!

The page I need help with: [log in to see the link]


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