Error adding registration form

I am having an unknown error while adding a custom registration form.Can you help me to fix t as I have already done what I can do with the code and now I am totally stuck what to do

function wooc_validate_extra_register_fields( $username, $email, $validation_errors ) {
      if ( isset( $_POST['billing_first_name'] ) && empty( $_POST['billing_first_name'] ) ) {
             $validation_errors->add( 'billing_first_name_error', __( '<strong>Error</strong>: First name is required!', 'woocommerce' ) );
      }
      if ( isset( $_POST['billing_last_name'] ) && empty( $_POST['billing_last_name'] ) ) {
             $validation_errors->add( 'billing_last_name_error', __( '<strong>Error</strong>: Last name is required!.', 'woocommerce' ) );
      }
         return $validation_errors;
}
add_action( 'woocommerce_register_post', 'wooc_validate_extra_register_fields', 10, 3 );

I have seen the code here https://www.cloudways.com/blog/add-woocommerce-registration-form-fields/