Invoice For WooCommerce: PO as Required Field

patch.diff

diff --git a/Models/Gateways/IGFW_Invoice_Gateway.php b/Models/Gateways/IGFW_Invoice_Gateway.php
index 1253db2..c047ab7 100644
--- a/Models/Gateways/IGFW_Invoice_Gateway.php
+++ b/Models/Gateways/IGFW_Invoice_Gateway.php
@@ -136,7 +136,7 @@ class IGFW_Invoice_Gateway extends \WC_Payment_Gateway {
 
         if (get_option('igfw_enable_purchase_order_number') == 'yes') {
 
-            echo '<p><b>' . __('Purchase Order (optional)', 'invoice-gateway-for-woocommerce') . '</b></p>';
+            echo '<p><b>' . __('Purchase Order', 'invoice-gateway-for-woocommerce') . '</b></p>';
             echo '<p><input type="text" name="igfw_purchase_order_number" placeholder="PO Number"></p>';
             echo '<p>' . __('We will generate and send you an invoice for your order, if you have a PO number, please enter it.', 'invoice-gateway-for-woocommerce') . '</p>';
 
@@ -149,6 +149,17 @@ class IGFW_Invoice_Gateway extends \WC_Payment_Gateway {
 
     }
 
+       public function validate_fields() {
+               if (get_option('igfw_enable_purchase_order_number') == 'yes') {
+                       if (strlen($_POST['igfw_purchase_order_number'] ?: '') == 0) {
+                               wc_add_notice('<strong>Purchase Order Number</strong> is a required field.', 'error' );
+                               return false;
+                       }
+               }
+
+               return true;
+       }
+
     /**
      * Check If The Gateway Is Available For Use.
      *