diff --git a/src/Models/Attachments/Buttons/Inline/OpenAppButton.php b/src/Models/Attachments/Buttons/Inline/OpenAppButton.php
index 4d5c2a1..fd671df 100644
--- a/src/Models/Attachments/Buttons/Inline/OpenAppButton.php
+++ b/src/Models/Attachments/Buttons/Inline/OpenAppButton.php
@@ -13,17 +13,20 @@
 {
     public ?string $webApp;
     public ?int $contactId;
+    public ?string $payload;
 
     /**
      * @param string $text Visible button text (1 to 128 characters).
      * @param string|null $webApp The public name (username) of the bot or a link to it, whose mini-application should be launched.
      * @param int|null $contactId The ID of the bot whose mini-app should be launched.
+     * @param string|null $payload Init param which would be passed in mini-application initData (1 to 512 characters, allowed A-Z, a-z, 0-9, _(underscore) , - (minus) ).
      */
-    public function __construct(string $text, ?string $webApp = null, ?int $contactId = null)
+    public function __construct(string $text, ?string $webApp = null, ?int $contactId = null, ?string $payload = null)
     {
         parent::__construct(InlineButtonType::OpenApp, $text);
 
         $this->webApp = $webApp;
         $this->contactId = $contactId;
+        $this->payload = $payload;
     }
 }
diff --git a/tests/Models/Attachments/Buttons/Inline/OpenAppButtonTest.php b/tests/Models/Attachments/Buttons/Inline/OpenAppButtonTest.php
index 0801cdc..3a1e8f0 100644
--- a/tests/Models/Attachments/Buttons/Inline/OpenAppButtonTest.php
+++ b/tests/Models/Attachments/Buttons/Inline/OpenAppButtonTest.php
@@ -16,11 +16,12 @@ final class OpenAppButtonTest extends TestCase
     #[Test]
     public function toArraySerializesCorrectly(): void
     {
-        $button = new OpenAppButton('Test Button', 'MyWebApp', 123);
+        $button = new OpenAppButton('Test Button', 'MyWebApp', 123, 'somePayload');
 
         $expectedArray = [
             'web_app' => 'MyWebApp',
             'contact_id' => 123,
+            'payload' => 'somePayload',
             'type' => InlineButtonType::OpenApp->value,
             'text' => 'Test Button',
         ];
@@ -38,6 +39,7 @@ public function fromArrayHydratesCorrectly(): void
             'text' => 'Launch',
             'web_app' => 'SomeApp',
             'contact_id' => 456,
+            'payload' => 'somePayload'
         ];
 
         $button = OpenAppButton::fromArray($data);
@@ -47,5 +49,6 @@ public function fromArrayHydratesCorrectly(): void
         $this->assertSame('Launch', $button->text);
         $this->assertSame('SomeApp', $button->webApp);
         $this->assertSame(456, $button->contactId);
+        $this->assertSame('somePayload', $button->payload);
     }
 }