khaledsaikat

<?php
/*
Plugin Name: Frontend AJAX Sub-Category Dropdown
Plugin URI: http://khaledsaikat.com
Description: Load sub-category dropdown based on parent category by ajax call
Version: 0.1
Author: Khaled Hossain
Author URI: http://khaledsaikat.com
*/

Pross

<?php
add_action( 'user_register', 'add_user_to_sendy_list' );

function add_user_to_sendy_list( $user_id ) {
  $list = 'SENDY_LIST_ID';
  $url  = 'http://SENDY_INSTALL_URL/subscribe';
  $user = get_userdata( $user_id );
  
  $email = $user->data->user_email;
  $name  = $user->data->user_nicename;

regularguy01

<?php
/*
Original code by Pross found here https://gist.github.com/Pross/3ff9f68fea20dcdc8845919dc51de90d
//-------------------------------------------------------------------------------------//
Version 1.0.0
bdacus01 2020 found here https://gist.github.com/bdacus01/84171d9454e7ab4152be2edc65855c21
Improvements to code: added api key, firstname, and customer filter list.
If new account doesn't have the first_name filled in pull it from the registration POST.  
user_register does not write out to the database until after registration is complete. 
This code is for WC Customers.  We are assuming they bought products or created an account.