MailChimp strongly recommends against single opt-ins, so instead of adding a setting for that, we decided to go with a filter. Add this filter to your functions.php file to disable double opt-ins…
add_filter( 'fl_builder_mailchimp_double_option', '__return_false' );
Additionally, you can add this filter to your functions.php file to disable the welcome message…
add_filter( 'fl_builder_mailchimp_welcome', '__return_false' );
You can read more about these on our Filter Reference page.
Those aren’t live yet but will be available in the next update that should be out next week. Keep an eye out for that!