diff --git a/src/LaravelGoogleShoppingFeed.php b/src/LaravelGoogleShoppingFeed.php
index d0592b2..868c0b0 100644
--- a/src/LaravelGoogleShoppingFeed.php
+++ b/src/LaravelGoogleShoppingFeed.php
@@ -11,13 +11,13 @@
 
 class LaravelGoogleShoppingFeed
 {
-    public string $title = '';
-    public string $description = '';
-    public string $link = '';
+    public readonly string $title;
+    public readonly string $description;
+    public readonly string $link;
 
     protected array $products = [];
 
-    protected array $requiredProductFields = [
+    protected const array REQUIRED_PRODUCT_FIELDS = [
         'id',
         'link',
         'title',
@@ -35,17 +35,15 @@ public static function init(string $title = '', string $description = '', string
         return $feed;
     }
 
-    public function addItem(array $item): bool
+    public function addItem(array $item): void
     {
-        foreach ($this->requiredProductFields as $field) {
+        foreach (self::REQUIRED_PRODUCT_FIELDS as $field) {
             if (! isset($item[$field])) {
                 throw new MissingRequiredFieldException("Required field '{$field}' is missing");
             }
         }
 
         $this->products[] = $item;
-
-        return true;
     }
 
     public function toXml(): string
@@ -70,6 +68,8 @@ public function toXml(): string
 
         $xml = ArrayToXml::convert($data, '');
         $xml = str_replace(['    ', '<root>', '</root>', "\n", "\r", '<remove>remove</remove>'], '', $xml);
+        // spatie/array-to-xml does not support repeated keys, so products are keyed as
+        // item_0, item_1, etc. and renamed back to <item> tags here.
         $xml = (string) preg_replace('/item_\d+/', 'item', $xml);
 
         return $xml;
@@ -77,6 +77,6 @@ public function toXml(): string
 
     public function generate(): Response
     {
-        return ResponseFacade::make($this->toXml(), 200, ['Content-Type' => 'text/xml']);
+        return ResponseFacade::make($this->toXml(), headers: ['Content-Type' => 'application/rss+xml']);
     }
 }