diff --git a/composer.json b/composer.json
index 4cd891d..85ece47 100644
--- a/composer.json
+++ b/composer.json
@@ -1,7 +1,7 @@
 {
     "name": "xendit/xendit-php",
     "description": "PHP clients for Xendit API",
-    "version": "2.9.0",
+    "version": "2.9.1",
     "license": "MIT",
     "keywords": [
         "xendit"
diff --git a/composer.lock b/composer.lock
index 10aca3b..7b32bce 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "d1513a01ab68168e6b8d2ab07c563b10",
+    "content-hash": "a95d3dc0df12e2cb23503981c7da6915",
     "packages": [
         {
             "name": "guzzlehttp/guzzle",
@@ -110,16 +110,16 @@
         },
         {
             "name": "guzzlehttp/promises",
-            "version": "1.4.0",
+            "version": "1.4.1",
             "source": {
                 "type": "git",
                 "url": "https://github.com/guzzle/promises.git",
-                "reference": "60d379c243457e073cff02bc323a2a86cb355631"
+                "reference": "8e7d04f1f6450fef59366c399cfad4b9383aa30d"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/guzzle/promises/zipball/60d379c243457e073cff02bc323a2a86cb355631",
-                "reference": "60d379c243457e073cff02bc323a2a86cb355631",
+                "url": "https://api.github.com/repos/guzzle/promises/zipball/8e7d04f1f6450fef59366c399cfad4b9383aa30d",
+                "reference": "8e7d04f1f6450fef59366c399cfad4b9383aa30d",
                 "shasum": ""
             },
             "require": {
@@ -159,9 +159,9 @@
             ],
             "support": {
                 "issues": "https://github.com/guzzle/promises/issues",
-                "source": "https://github.com/guzzle/promises/tree/1.4.0"
+                "source": "https://github.com/guzzle/promises/tree/1.4.1"
             },
-            "time": "2020-09-30T07:37:28+00:00"
+            "time": "2021-03-07T09:25:29+00:00"
         },
         {
             "name": "guzzlehttp/psr7",
@@ -578,16 +578,16 @@
         },
         {
             "name": "phar-io/version",
-            "version": "3.0.4",
+            "version": "3.1.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/phar-io/version.git",
-                "reference": "e4782611070e50613683d2b9a57730e9a3ba5451"
+                "reference": "bae7c545bef187884426f042434e561ab1ddb182"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/phar-io/version/zipball/e4782611070e50613683d2b9a57730e9a3ba5451",
-                "reference": "e4782611070e50613683d2b9a57730e9a3ba5451",
+                "url": "https://api.github.com/repos/phar-io/version/zipball/bae7c545bef187884426f042434e561ab1ddb182",
+                "reference": "bae7c545bef187884426f042434e561ab1ddb182",
                 "shasum": ""
             },
             "require": {
@@ -623,9 +623,9 @@
             "description": "Library for handling version information and constraints",
             "support": {
                 "issues": "https://github.com/phar-io/version/issues",
-                "source": "https://github.com/phar-io/version/tree/3.0.4"
+                "source": "https://github.com/phar-io/version/tree/3.1.0"
             },
-            "time": "2020-12-13T23:18:30+00:00"
+            "time": "2021-02-23T14:00:09+00:00"
         },
         {
             "name": "phpdocumentor/reflection-common",
@@ -2102,7 +2102,7 @@
         },
         {
             "name": "symfony/polyfill-ctype",
-            "version": "v1.22.0",
+            "version": "v1.22.1",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/polyfill-ctype.git",
@@ -2161,7 +2161,7 @@
                 "portable"
             ],
             "support": {
-                "source": "https://github.com/symfony/polyfill-ctype/tree/v1.22.0"
+                "source": "https://github.com/symfony/polyfill-ctype/tree/v1.22.1"
             },
             "funding": [
                 {
@@ -2309,30 +2309,35 @@
         },
         {
             "name": "webmozart/assert",
-            "version": "1.9.1",
+            "version": "1.10.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/webmozarts/assert.git",
-                "reference": "bafc69caeb4d49c39fd0779086c03a3738cbb389"
+                "reference": "6964c76c7804814a842473e0c8fd15bab0f18e25"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/webmozarts/assert/zipball/bafc69caeb4d49c39fd0779086c03a3738cbb389",
-                "reference": "bafc69caeb4d49c39fd0779086c03a3738cbb389",
+                "url": "https://api.github.com/repos/webmozarts/assert/zipball/6964c76c7804814a842473e0c8fd15bab0f18e25",
+                "reference": "6964c76c7804814a842473e0c8fd15bab0f18e25",
                 "shasum": ""
             },
             "require": {
-                "php": "^5.3.3 || ^7.0 || ^8.0",
+                "php": "^7.2 || ^8.0",
                 "symfony/polyfill-ctype": "^1.8"
             },
             "conflict": {
                 "phpstan/phpstan": "<0.12.20",
-                "vimeo/psalm": "<3.9.1"
+                "vimeo/psalm": "<4.6.1 || 4.6.2"
             },
             "require-dev": {
-                "phpunit/phpunit": "^4.8.36 || ^7.5.13"
+                "phpunit/phpunit": "^8.5.13"
             },
             "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.10-dev"
+                }
+            },
             "autoload": {
                 "psr-4": {
                     "Webmozart\\Assert\\": "src/"
@@ -2356,9 +2361,9 @@
             ],
             "support": {
                 "issues": "https://github.com/webmozarts/assert/issues",
-                "source": "https://github.com/webmozarts/assert/tree/1.9.1"
+                "source": "https://github.com/webmozarts/assert/tree/1.10.0"
             },
-            "time": "2020-07-08T17:02:28+00:00"
+            "time": "2021-03-09T10:59:23+00:00"
         }
     ],
     "aliases": [],
diff --git a/src/ApiOperations/Retrieve.php b/src/ApiOperations/Retrieve.php
index 4ca28fe..d9f2b54 100644
--- a/src/ApiOperations/Retrieve.php
+++ b/src/ApiOperations/Retrieve.php
@@ -27,7 +27,7 @@ trait Retrieve
     /**
      * Send GET request to retrieve data
      *
-     * @param int|null $id ID
+     * @param string|null $id ID
      *
      * @return array
      */