diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 53f73ce..268fd33 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-version: ['7.0', '7.1', '7.2', '7.3', '7.4']
+        php-version: ['7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
     steps:
       - uses: actions/checkout@v2
       - name: Setup PHP ${{ matrix.php-version }}
diff --git a/composer.json b/composer.json
index dd85e01..17c5ad5 100644
--- a/composer.json
+++ b/composer.json
@@ -16,10 +16,10 @@
         "ext-curl": "*",
         "ext-json": "*",
         "ext-fileinfo": "*",
-        "symfony/dotenv": "3.4.*"
+        "symfony/dotenv": "3.4.*|6.4.*"
     },
     "require-dev": {
-        "phpunit/phpunit": "6.*",
+        "phpunit/phpunit": "6.*|8.*",
         "squizlabs/php_codesniffer": "3.*"
     },
     "support": {
diff --git a/lib/RetailCrm/Response/ApiResponse.php b/lib/RetailCrm/Response/ApiResponse.php
index a8a4af4..2cb9c2a 100644
--- a/lib/RetailCrm/Response/ApiResponse.php
+++ b/lib/RetailCrm/Response/ApiResponse.php
@@ -171,6 +171,7 @@ class ApiResponse implements \ArrayAccess
      * @throws \BadMethodCallException
      * @return void
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         throw new \BadMethodCallException('This activity not allowed');
@@ -184,6 +185,7 @@ class ApiResponse implements \ArrayAccess
      * @throws \BadMethodCallException
      * @return void
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         throw new \BadMethodCallException('This call not allowed');
@@ -196,6 +198,7 @@ class ApiResponse implements \ArrayAccess
      *
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return isset($this->response[$offset]);
@@ -210,6 +213,7 @@ class ApiResponse implements \ArrayAccess
      *
      * @return mixed
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         if (!isset($this->response[$offset])) {