Set customer "exempt of vat" when order is created in backend in WooCommerce

Question

I would like to add an action in woocommerce to remove the tax from orders when created in the backend and for special users as customers.

This code is working for the normal order process on the website, but not on the backend

add_action( 'woocommerce_checkout_update_order_review', 'remove_tax_from_user' );
add_action( 'woocommerce_before_cart_contents', 'remove_tax_from_user' );

function remove_tax_from_user( $post_data ) {
  global $woocommerce;
  $username = $woocommerce->customer->get_username();
  $user = get_user_by('login',$username);
  if($user)
  { 
    if( get_field('steuer_befreit', "user_{$user->ID}") ):
    $woocommerce->customer->set_is_vat_exempt( true );
    endif;
  }
}

Answer 1

In backend customer needs to be "exempt of Vat" before clicking on "Add order" .

You could try to use the hook save_post_shop_order that is triggered before order data is saved in backend, this way:

add_action( 'save_post_shop_order', 'backend_remove_tax_from_user', 50, 3 );
function backend_remove_tax_from_user( $post_id, $post, $update ) {

    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
        return $post_id; // Exit if it's an autosave

    if ( $post->post_status != 'publish' )
        return $post_id; // Exit if not 'publish' post status

    if ( ! current_user_can( 'edit_order', $post_id ) )
        return $post_id; // Exit if user is not allowed

    if( ! isset($_POST['customer_user']) ) return $post_id; // Exit

    if( $_POST['customer_user'] > 0 ){
        $customer_id = intval($_POST['customer_user']);
        if( get_field('steuer_befreit', "user_{$customer_id}") ){
            $wc_customer = new WC_Customer( $customer_id );
            $wc_customer->set_is_vat_exempt( true );
        }
    }
}

Code goes in function.php file of your active child theme (or theme).

But this will not work and you will not be able with any exiting hook to make that work. The only way Is to make first customer exempt of vat, then you can Add an order for this customer.