Adding a dummy email address at customer creation

functions.php

<?php 

function my_custom_create_customer_data($data){
  if(function_exists('is_pos') && is_pos()){
    $dummy_email = 'email@example.com'; // note: you would have to generate a unique email address for each user
    $data['email'] = ! isset($data['email']) || empty($data['email']) ? $dummy_email : $data['email'];
  };
  return $data;
}

add_filter('woocommerce_api_create_customer_data', 'my_custom_create_customer_data');