Add custom field to checkout page

functions.php

/**
 * Add the field to the checkout page
 */
add_action( 'woocommerce_after_order_notes', 'some_custom_checkout_field' );
 
function some_custom_checkout_field( $checkout ) {
 
    echo '<div id="some_custom_checkout_field"><h2>' . __('My Field Header') . '</h2>';
 
    woocommerce_form_field( 'some_field_name', array(
        'type'          => 'text',
        'class'         => array('my-field-class form-row-wide'),
        'label'         => __('My Field Label'),
        'placeholder'   => __('Some placeholder text to guide the customer'),
        'required'      => true,
        ), $checkout->get_value( 'some_field_name' ));
 
    echo '</div>';
 
}