Hi,
If you can add custom fields to a form in WordPress (any form) and give them those names (mc4wp-***) you can use the Custom Integration method and it will work.
https://kb.mc4wp.com/add-sign-checkbox-custom-form/
But, in the case of WP Forms, you can’t do that, because WP Forms generates its own field names, like wpforms[fields][1][first]. So the next best thing is to add some custom code, here is an example: https://github.com/ibericode/mc4wp-snippets/blob/master/integrations/send-name-field-from-wpforms.php
Of course you need to adapt that code to your own MailChimp merge tags and WP forms field names. You can see the field names WP Forms generated when you inspect the code on your site.
Hope that helps. If you have any questions, please let me know!
