WooCommerce - Don't allow PO BOX within postcode, address 1 or address 2 fields.

gistfile1.txt

add_action('woocommerce_after_checkout_validation', 'deny_pobox_postcode');

function deny_pobox_postcode( $posted ) {
  global $woocommerce;
  
  // Put postcode, address 1 and address 2 into an array
  $check_address  = array();
  $check_address[] = isset( $posted['shipping_postcode'] ) ? $posted['shipping_postcode'] : $posted['billing_postcode'];
  $check_address[] = isset( $posted['shipping_address_1'] ) ? $posted['shipping_address_1'] : $posted['billing_address_1'];
  $check_address[] = isset( $posted['shipping_address_2'] ) ? $posted['shipping_address_2'] : $posted['billing_address_2'];

  // Implode address, make lowercase, and remove spaces and full stops
  $check_address = strtolower( str_replace( array( ' ', '.' ), '', implode( '-', $check_address ) ) );

  if ( strstr( $check_address, 'pobox' ) ) {
    $woocommerce->add_error( "Sorry, we don't ship to PO BOX addresses." );
  }
}

Mike,

Is there a way to use this code to where the message pops up only when they try to use a certain shipping method? For example the UPS method. I want to deny shipping to PO Box Addresses based on the shipping method UPS.