[WooCommerce 3.0+] Preventing PO box shipping

wc-no-po-box-shipping.php

add_action('woocommerce_after_checkout_validation', 'deny_pobox_postcode');

function deny_pobox_postcode( $posted ) {
  global $woocommerce;

  $address  = ( isset( $posted['shipping_address_1'] ) ) ? $posted['shipping_address_1'] : $posted['billing_address_1'];
  $postcode = ( isset( $posted['shipping_postcode'] ) ) ? $posted['shipping_postcode'] : $posted['billing_postcode'];

  $replace  = array(" ", ".", ",");
  $address  = strtolower( str_replace( $replace, '', $address ) );
  $postcode = strtolower( str_replace( $replace, '', $postcode ) );

  if ( strstr( $address, 'pobox' ) || strstr( $postcode, 'pobox' ) ) {
    wc_add_notice( sprintf( __( "Sorry, we cannot ship to PO BOX addresses.") ) ,'error' );
  }
}

This doesn't prevent the order from going through for us. It does give them the notice "Sorry, we cannot ship to PO BOX addresses." but the order has already gone through. I'm wondering if the timing is correct? Seems like woocommerce_after_checkout_validation might be too late in process. Is there anything like woocommerce_before_checkout_validation that might work better?

any luck with a solution?