Add a Custom Checkout Field

For the developer

1. Add below codes to your theme's bottom of the functions.php file

2. If you are using child-theme please add codes ***-child/functions.php

a. Add new field to checkout

add_action( 'woocommerce_before_order_notes', 'optimum7_custom_checkout_field' );

function optimum7_custom_checkout_field( $checkout ) { 
   $current_user = wp_get_current_user();
   $saved_license_no = $current_user->license_no;
   woocommerce_form_field( 'license_no', array(        
      'type' => 'text',        
      'class' => array( 'form-row-wide' ),        
      'label' => 'License Number',        
      'placeholder' => 'CA12345678',        
      'required' => true,        
      'default' => $saved_license_no,        
   ), $checkout->get_value( 'license_no' ) ); 
}

b. Validate New Field

add_action( 'woocommerce_checkout_process', 'optimum7_validate_new_checkout_field' );

function optimum7_validate_new_checkout_field() {    
   if ( ! $_POST['license_no'] ) {
      wc_add_notice( 'Please enter your Licence Number', 'error' );
   }
}

c. Save & Show New Field Orders & Emails

add_action( 'woocommerce_checkout_update_order_meta', 'optimum7_save_new_checkout_field' );

function optimum7_save_new_checkout_field( $order_id ) { 
    if ( $_POST['license_no'] ) update_post_meta( $order_id, '_license_no', esc_attr( $_POST['license_no'] ) );
}

add_action( 'woocommerce_admin_order_data_after_billing_address', 'optimum7_show_new_checkout_field_order', 10, 1 );

function optimum7_show_new_checkout_field_order( $order ) {    
   $order_id = $order->get_id();
   if ( get_post_meta( $order_id, '_license_no', true ) ) echo '<p><strong>License Number:</strong> ' . get_post_meta( $order_id, '_license_no', true ) . '</p>';
}

add_action( 'woocommerce_email_after_order_table', 'optimum7_show_new_checkout_field_emails', 20, 4 );

function optimum7_show_new_checkout_field_emails( $order, $sent_to_admin, $plain_text, $email ) {
    if ( get_post_meta( $order->get_id(), '_license_no', true ) ) echo '<p><strong>License Number:</strong> ' . get_post_meta( $order->get_id(), '_license_no', true ) . '</p>';
}