diff --git a/changelog.txt b/changelog.txt
index 613c7c6..199d49e 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -1,5 +1,10 @@
 ** Hellotext for WooCommerce Changelog **
 
+2026-01-19 - version 1.3.1
+
+* Add X-Plugin-Version header to all API requests for version tracking and analytics.
+
+
 2026-01-18 - version 1.3.0
 
 * Add comprehensive type hints to all source files for better IDE support and type safety.
diff --git a/hellotext.php b/hellotext.php
index 4fb9c48..642383a 100644
--- a/hellotext.php
+++ b/hellotext.php
@@ -8,7 +8,7 @@
  * Plugin Name: Hellotext
  * Plugin URI: https://github.com/hellotext/hellotext-wordpress
  * Description: Integrates Hellotext tracking to WooCommerce.
- * Version: 1.3.0
+ * Version: 1.3.1
  * Author: Hellotext
  * Author URI: https://www.hellotext.com
  * License: GPL v2
diff --git a/src/Api/Client.php b/src/Api/Client.php
index e0db10b..883b8f0 100644
--- a/src/Api/Client.php
+++ b/src/Api/Client.php
@@ -53,6 +53,7 @@ public static function request(string $method = 'GET', string $path = '/', array
             'headers' => [
                 'Content-Type' => 'application/json',
                 'Authorization' => 'Bearer ' . $access_token,
+                'X-Plugin-Version' => self::get_plugin_version(),
             ],
             'sslverify' => true,
         ];
@@ -178,4 +179,20 @@ private static function get_api_url(): string {
         return $HELLOTEXT_API_URL . self::$sufix;
     }
 
+    /**
+     * Get plugin version.
+     *
+     * @return string
+     */
+    private static function get_plugin_version(): string {
+        if (!function_exists('get_plugin_data')) {
+            require_once ABSPATH . 'wp-admin/includes/plugin.php';
+        }
+
+        $plugin_file = dirname(__DIR__, 2) . '/hellotext.php';
+        $plugin_data = get_plugin_data($plugin_file, false, false);
+
+        return $plugin_data['Version'] ?? 'unknown';
+    }
+
 }
diff --git a/tests/Mocks.php b/tests/Mocks.php
index f677503..f045b0d 100644
--- a/tests/Mocks.php
+++ b/tests/Mocks.php
@@ -175,6 +175,11 @@ public function get_id () {
 // Mock WordPress HTTP API functions
 if (!function_exists('wp_remote_request')) {
 	function wp_remote_request ($url, $args = array()) {
+		// Allow per-test override
+		if (isset($GLOBALS['test_wp_remote_request'])) {
+			return $GLOBALS['test_wp_remote_request']($url, $args);
+		}
+
 		return array(
 			'response' => array('code' => 200),
 			'body' => json_encode(array('success' => true)),
@@ -211,3 +216,34 @@ function wp_remote_retrieve_body ($response) {
 		return $response['body'] ?? '';
 	}
 }
+
+if (!function_exists('get_option')) {
+	function get_option ($option, $default = false) {
+		// Allow per-test override
+		if (isset($GLOBALS['test_options'][$option])) {
+			return $GLOBALS['test_options'][$option];
+		}
+
+		// Default mock values
+		if ($option === 'hellotext_access_token') {
+			return 'test_token_123';
+		}
+
+		return $default;
+	}
+}
+
+if (!function_exists('get_plugin_data')) {
+	function get_plugin_data ($plugin_file, $markup = true, $translate = true) {
+		// Allow per-test override
+		if (isset($GLOBALS['test_plugin_data'])) {
+			return $GLOBALS['test_plugin_data'];
+		}
+
+		return [
+			'Name' => 'Hellotext',
+			'Version' => '1.3.0',
+			'Author' => 'Hellotext',
+		];
+	}
+}
diff --git a/tests/Unit/Api/ClientTest.php b/tests/Unit/Api/ClientTest.php
new file mode 100644
index 0000000..8dbe7e1
--- /dev/null
+++ b/tests/Unit/Api/ClientTest.php
@@ -0,0 +1,137 @@
+<?php
+
+use Hellotext\Api\Client;
+use Hellotext\Constants;
+
+beforeEach(function () {
+    if (!defined('ABSPATH')) {
+        define('ABSPATH', '/tmp/wordpress/');
+    }
+
+    global $HELLOTEXT_API_URL;
+    $HELLOTEXT_API_URL = 'https://api.hellotext.com';
+});
+
+test('Client has correct API version suffix by default', function () {
+    expect(Client::$sufix)->toBe('/v1');
+});
+
+test('can set custom suffix', function () {
+    Client::with_sufix('/v2');
+    expect(Client::$sufix)->toBe('/v2');
+
+    // Reset
+    Client::with_sufix('/v1');
+});
+
+test('custom suffix adds leading slash if missing', function () {
+    Client::with_sufix('v3');
+    expect(Client::$sufix)->toBe('/v3');
+
+    // Reset
+    Client::with_sufix('/v1');
+});
+
+test('empty suffix works', function () {
+    Client::with_sufix('');
+    expect(Client::$sufix)->toBe('');
+
+    // Reset
+    Client::with_sufix('/v1');
+});
+
+test('Client::get() returns expected structure', function () {
+    $response = Client::get('/test');
+
+    expect($response)->toBeArray();
+    expect($response)->toHaveKeys(['request', 'status', 'body', 'error']);
+});
+
+test('Client::post() returns expected structure', function () {
+    $response = Client::post('/test', ['data' => 'value']);
+
+    expect($response)->toBeArray();
+    expect($response)->toHaveKeys(['request', 'status', 'body', 'error']);
+});
+
+test('Client::put() returns expected structure', function () {
+    $response = Client::put('/test/1', ['data' => 'value']);
+
+    expect($response)->toBeArray();
+    expect($response)->toHaveKeys(['request', 'status', 'body', 'error']);
+});
+
+test('Client::patch() returns expected structure', function () {
+    $response = Client::patch('/test/1', ['data' => 'value']);
+
+    expect($response)->toBeArray();
+    expect($response)->toHaveKeys(['request', 'status', 'body', 'error']);
+});
+
+test('Client::delete() returns expected structure', function () {
+    $response = Client::delete('/test/1');
+
+    expect($response)->toBeArray();
+    expect($response)->toHaveKeys(['request', 'status', 'body', 'error']);
+});
+
+test('request includes method in response', function () {
+    $response = Client::get('/test');
+
+    expect($response['request']['method'])->toBe('GET');
+});
+
+test('request includes path in response', function () {
+    $response = Client::get('/test/endpoint');
+
+    expect($response['request']['path'])->toContain('/test/endpoint');
+});
+
+test('request includes data in response', function () {
+    $data = ['key' => 'value'];
+    $response = Client::post('/test', $data);
+
+    expect($response['request']['data'])->toBe($data);
+});
+
+test('with_sufix returns Client instance', function () {
+    $client = Client::with_sufix('/custom');
+
+    expect($client)->toBeInstanceOf(Client::class);
+});
+
+test('all HTTP methods accept optional data parameter', function () {
+    // These should not throw errors
+    expect(fn() => Client::get('/test', null))->not->toThrow(Error::class);
+    expect(fn() => Client::post('/test', null))->not->toThrow(Error::class);
+    expect(fn() => Client::put('/test', null))->not->toThrow(Error::class);
+    expect(fn() => Client::patch('/test', null))->not->toThrow(Error::class);
+    expect(fn() => Client::delete('/test', null))->not->toThrow(Error::class);
+});
+
+test('handles empty path gracefully', function () {
+    $response = Client::get('');
+
+    expect($response)->toBeArray();
+    expect($response)->toHaveKey('status');
+});
+
+test('request method is case-insensitive', function () {
+    $response = Client::request('get', '/test');
+    expect($response['request']['method'])->toBe('get');
+});
+
+test('static methods can be called', function () {
+    expect(method_exists(Client::class, 'get'))->toBeTrue();
+    expect(method_exists(Client::class, 'post'))->toBeTrue();
+    expect(method_exists(Client::class, 'put'))->toBeTrue();
+    expect(method_exists(Client::class, 'patch'))->toBeTrue();
+    expect(method_exists(Client::class, 'delete'))->toBeTrue();
+    expect(method_exists(Client::class, 'request'))->toBeTrue();
+    expect(method_exists(Client::class, 'with_sufix'))->toBeTrue();
+});
+
+test('Client has API_VERSION constant reference', function () {
+    expect(defined('Hellotext\Constants::API_VERSION'))->toBeTrue();
+    expect(Constants::API_VERSION)->toBe('v1');
+});