gistfile1.php

<?php

/**
 * Add checkbox field to the checkout
 **/
add_action('woocommerce_after_order_notes', 'my_custom_checkout_field');
 
function my_custom_checkout_field( $checkout ) {
 
    echo '<div id="my-new-field"><h3>'.__('My Checkbox: ').'</h3>';
 
    woocommerce_form_field( 'my_checkbox', array(
        'type'          => 'checkbox',
        'class'         => array('input-checkbox'),
        'label'         => __('I have read and agreed.'),
        'required'  => true,
        ), $checkout->get_value( 'my_checkbox' ));
 
    echo '</div>';
}
 
/**
 * Process the checkout
 **/
add_action('woocommerce_checkout_process', 'my_custom_checkout_field_process');
 
function my_custom_checkout_field_process() {

    // Check if set, if its not set add an error.
    if (!$_POST['my_checkbox'])
         wc_add_notice( __('Please agree to my checkbox.'), 'error' );
}
 
/**
 * Update the order meta with field value
 **/
add_action('woocommerce_checkout_update_order_meta', 'my_custom_checkout_field_update_order_meta');
 
function my_custom_checkout_field_update_order_meta( $order_id ) {
    if ($_POST['my_checkbox']) update_post_meta( $order_id, 'My Checkbox', esc_attr($_POST['my_checkbox']));
}

?>