diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index c165d56..211e2a2 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        php: ['7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
+        php: ['7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1']
 
     steps:
       ## checkout the repoistory 
@@ -27,7 +27,7 @@ jobs:
         with:
           php-version: ${{ matrix.php }}
           extensions: apc, curl, dom, imagick, intl, mbstring, mcrypt, memcached, mysql, pdo, pdo_mysql, pdo_pgsql, pdo_sqlite, pgsql, sqlite
-          ini-values: date.timezone='UTC'
+          ini-values: date.timezone='UTC',error_reporting=E_ALL,display_errors=On
 
       ## install composer
       - name: Install dependencies
@@ -36,7 +36,7 @@ jobs:
       ## run unit tests
       - name: PHP Unit tests for PHP 
         run: vendor/bin/phpunit --verbose --configuration actions.phpunit.xml
-        if: matrix.php == '8.0' || matrix.php == '7.4' || matrix.php == '7.3' || matrix.php == '7.2' || matrix.php == '7.0'
+        if: matrix.php == '8.1' || matrix.php == '8.0' || matrix.php == '7.4' || matrix.php == '7.3' || matrix.php == '7.2' || matrix.php == '7.0'
 
       ## unit test with coverage
       - name: PHP Unit tests for PHP 7.1
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0009f1d..bdcc391 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## 2.9.1 (25. May 2022)
+
++ [#38](https://github.com/luyadev/luya-headless/pull/38) PHP 8.1 compatibility
+
 ## 2.9.0 (22. September 2021)
 
 + [#35](https://github.com/luyadev/luya-headless/pull/35) Added strict caching property which is by default enabled. Strict cache will only cache data which are from status 200 response code.
diff --git a/src/base/AbstractRequestClient.php b/src/base/AbstractRequestClient.php
index e595008..58b1a3d 100644
--- a/src/base/AbstractRequestClient.php
+++ b/src/base/AbstractRequestClient.php
@@ -210,7 +210,7 @@ public function setEndpoint($endpoint)
      */
     public function getRequestUrl()
     {
-        $parts = [rtrim($this->client->serverUrl, '/'), $this->client->language, ltrim($this->endpoint, '/')];
+        $parts = [rtrim($this->client->serverUrl, '/'), $this->client->language, ltrim((string) $this->endpoint, '/')];
         
         $url = implode("/", array_filter($parts));
 
diff --git a/src/base/BaseIterator.php b/src/base/BaseIterator.php
index dcf1c75..f14079a 100644
--- a/src/base/BaseIterator.php
+++ b/src/base/BaseIterator.php
@@ -120,6 +120,7 @@ public function addItem(array $item, $key)
      * {@inheritDoc}
      * @see Countable::count()
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         return count($this->data);
@@ -131,6 +132,7 @@ public function count()
      * {@inheritDoc}
      * @see Iterator::rewind()
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         return reset($this->data);
@@ -140,11 +142,16 @@ public function rewind()
      * {@inheritDoc}
      * @see Iterator::current()
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return current($this->data);
     }
     
+    /**
+     * {@inheritDoc}
+     */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return key($this->data);
@@ -154,6 +161,7 @@ public function key()
      * {@inheritDoc}
      * @see Iterator::next()
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         return next($this->data);
@@ -163,6 +171,7 @@ public function next()
      * {@inheritDoc}
      * @see Iterator::valid()
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         return key($this->data) !== null;
@@ -174,6 +183,7 @@ public function valid()
      * {@inheritDoc}
      * @see ArrayAccess::offsetSet()
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         $this->data[$offset] = $value;
@@ -183,6 +193,7 @@ public function offsetSet($offset, $value)
      * {@inheritDoc}
      * @see ArrayAccess::offsetExists()
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return isset($this->data[$offset]);
@@ -192,6 +203,7 @@ public function offsetExists($offset)
      * {@inheritDoc}
      * @see ArrayAccess::offsetUnset()
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         unset($this->data[$offset]);
@@ -201,6 +213,7 @@ public function offsetUnset($offset)
      * {@inheritDoc}
      * @see ArrayAccess::offsetGet()
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return isset($this->data[$offset]) ? $this->data[$offset] : null;