ACF Form Builder - Register Custom Action - Do your own thing after user press submit button

acf-form-builder-subscribe-via-mailchimp.php

<?php
/**
 * Subscribe via Mailchimp
 */

//Your function name must start with acf_fb_custom_actions_
function acf_fb_custom_actions_subscribe_via_mailchimp($data) {
	//We already had $data - you can var_dump() to see what is inside
  if ( is_null($data) )
		return;
	/* Prepre the form settings */
	$form_id = $data['group_id'];
	$group_meta = get_post_meta( $form_id );
	$form_settings = unserialize($group_meta['form_settings'][0]);

	/* Prepare fields data */
	if (isset($data['acf'])) // acf pro version
		$fields = $data['acf'];
	else // acf free version
		$fields = $data['fields'];

	$fields_object = array();
	foreach ($fields as $key => $field) {
		$fields_object[$key] = get_field_object($key);	
	}
	$email_subscribe = array();
	foreach ($fields_object as $key => $value) {
		$email_subscribe[$key]['name'] = $value['name'];
		$email_subscribe[$key]['field_type'] = $value['type'];
		$email_subscribe[$key]['value'] = $fields[$key];
		$email_subscribe[$key]['form_field_type'] = $value['form_field_type'];
	}
	$prepare = array();
	foreach ($email_subscribe as $key => $value) {
		if ('subscribe_email'==$value['form_field_type']) $prepare['subscribe_email'] = $value['value'];
		if ('custom'==$value['form_field_type']) $prepare['custom'][$key] = $value['value'];
 	}

 	/* Get Mailchimp APIs */
	$mailchimp_api = $form_settings['mailchimp_api'];
	$mailchimp_list_id = $form_settings['mailchimp_list_id'];

	/* Almost there */
	$status = 'subscribed'; // subscribed, cleaned, pending
	$args = array(
	'method' => 'PUT',
 	'headers' => array(
		'Authorization' => 'Basic ' . base64_encode( 'user:'. $api_key )
	),
	'body' => json_encode(array(
    	'email_address' => $prepare['subscribe_email'],
		'status'        => $status
	))
	);
	foreach ($prepare['subscribe_email'] as $email_subscribe_post => $email_adress) {
	$response = wp_remote_post( 'https://' . substr($api_key,strpos($api_key,'-')+1) . '.api.mailchimp.com/3.0/lists/' . $mailchimp_list_id . '/members/' . md5(strtolower($email_adress)), $args );
	}
 
  wp_redirect('https://codecanyon.net/item/acf-form-builder-multipurpose-frontend-form-submission/19611604', 301);
  exit;

}
add_action( 'acf_fb_custom_actions', 'acf_fb_custom_actions_subscribe_via_mailchimp' );

?>