diff --git a/.gitignore b/.gitignore
index e69de29..7579f74 100644
--- a/.gitignore
+++ b/.gitignore
@@ -0,0 +1,2 @@
+vendor
+composer.lock
diff --git a/composer.json b/composer.json
index 7be6538..23a81c7 100644
--- a/composer.json
+++ b/composer.json
@@ -29,7 +29,7 @@
         "ext-json": "*",
         "ext-mbstring": "*",
         "guzzlehttp/guzzle": "^6.2 || ^7.0",
-        "guzzlehttp/psr7": "^1.8.2"
+        "guzzlehttp/psr7": "^1.8.2 || ^2.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^4.8",
diff --git a/src/com/amazon/paapi5/v1/api/DefaultApi.php b/src/com/amazon/paapi5/v1/api/DefaultApi.php
index f51d229..342a39b 100644
--- a/src/com/amazon/paapi5/v1/api/DefaultApi.php
+++ b/src/com/amazon/paapi5/v1/api/DefaultApi.php
@@ -207,7 +207,7 @@ public function getBrowseNodesWithHttpInfo($getBrowseNodesRequest)
     /**
      * Operation getBrowseNodesAsync
      *
-     * 
+     *
      *
      * @param  \Amazon\ProductAdvertisingAPI\v1\com\amazon\paapi5\v1\GetBrowseNodesRequest $getBrowseNodesRequest GetBrowseNodesRequest (required)
      *
@@ -227,7 +227,7 @@ function ($response) {
     /**
      * Operation getBrowseNodesAsyncWithHttpInfo
      *
-     * 
+     *
      *
      * @param  \Amazon\ProductAdvertisingAPI\v1\com\amazon\paapi5\v1\GetBrowseNodesRequest $getBrowseNodesRequest GetBrowseNodesRequest (required)
      *
@@ -341,7 +341,7 @@ protected function getBrowseNodesRequest($getBrowseNodesRequest)
             $httpBody = $_tempBody;
             // \stdClass has no __toString(), so we should encode it manually
             if ($httpBody instanceof \stdClass && $headers['Content-Type'] === 'application/json') {
-                $httpBody = \GuzzleHttp\json_encode($httpBody);
+                $httpBody = \GuzzleHttp\Utils::jsonEncode($httpBody);
             }
         } elseif (count($formParams) > 0) {
             if ($multipart) {
@@ -356,11 +356,11 @@ protected function getBrowseNodesRequest($getBrowseNodesRequest)
                 $httpBody = new MultipartStream($multipartContents);
 
             } elseif ($headers['Content-Type'] === 'application/json') {
-                $httpBody = \GuzzleHttp\json_encode($formParams);
+                $httpBody = \GuzzleHttp\Utils::jsonEncode($formParams);
 
             } else {
                 // for HTTP post (form)
-                $httpBody = \GuzzleHttp\Psr7\build_query($formParams);
+                $httpBody = \GuzzleHttp\Psr7\Query::build($formParams);
             }
         }
 
@@ -378,7 +378,7 @@ protected function getBrowseNodesRequest($getBrowseNodesRequest)
             $headers
         );
 
-        $query = \GuzzleHttp\Psr7\build_query($queryParams);
+        $query = \GuzzleHttp\Psr7\Query::build($queryParams);
         return new Request(
             'POST',
             $this->config->getHost() . $resourcePath . ($query ? "?{$query}" : ''),
@@ -519,7 +519,7 @@ public function getItemsWithHttpInfo($getItemsRequest)
     /**
      * Operation getItemsAsync
      *
-     * 
+     *
      *
      * @param  \Amazon\ProductAdvertisingAPI\v1\com\amazon\paapi5\v1\GetItemsRequest $getItemsRequest GetItemsRequest (required)
      *
@@ -539,7 +539,7 @@ function ($response) {
     /**
      * Operation getItemsAsyncWithHttpInfo
      *
-     * 
+     *
      *
      * @param  \Amazon\ProductAdvertisingAPI\v1\com\amazon\paapi5\v1\GetItemsRequest $getItemsRequest GetItemsRequest (required)
      *
@@ -653,7 +653,7 @@ protected function getItemsRequest($getItemsRequest)
             $httpBody = $_tempBody;
             // \stdClass has no __toString(), so we should encode it manually
             if ($httpBody instanceof \stdClass && $headers['Content-Type'] === 'application/json') {
-                $httpBody = \GuzzleHttp\json_encode($httpBody);
+                $httpBody = \GuzzleHttp\Utils::jsonEncode($httpBody);
             }
         } elseif (count($formParams) > 0) {
             if ($multipart) {
@@ -668,11 +668,11 @@ protected function getItemsRequest($getItemsRequest)
                 $httpBody = new MultipartStream($multipartContents);
 
             } elseif ($headers['Content-Type'] === 'application/json') {
-                $httpBody = \GuzzleHttp\json_encode($formParams);
+                $httpBody = \GuzzleHttp\Utils::jsonEncode($formParams);
 
             } else {
                 // for HTTP post (form)
-                $httpBody = \GuzzleHttp\Psr7\build_query($formParams);
+                $httpBody = \GuzzleHttp\Psr7\Query::build($formParams);
             }
         }
 
@@ -690,7 +690,7 @@ protected function getItemsRequest($getItemsRequest)
             $headers
         );
 
-        $query = \GuzzleHttp\Psr7\build_query($queryParams);
+        $query = \GuzzleHttp\Psr7\Query::build($queryParams);
         return new Request(
             'POST',
             $this->config->getHost() . $resourcePath . ($query ? "?{$query}" : ''),
@@ -831,7 +831,7 @@ public function getVariationsWithHttpInfo($getVariationsRequest)
     /**
      * Operation getVariationsAsync
      *
-     * 
+     *
      *
      * @param  \Amazon\ProductAdvertisingAPI\v1\com\amazon\paapi5\v1\GetVariationsRequest $getVariationsRequest GetVariationsRequest (required)
      *
@@ -851,7 +851,7 @@ function ($response) {
     /**
      * Operation getVariationsAsyncWithHttpInfo
      *
-     * 
+     *
      *
      * @param  \Amazon\ProductAdvertisingAPI\v1\com\amazon\paapi5\v1\GetVariationsRequest $getVariationsRequest GetVariationsRequest (required)
      *
@@ -965,7 +965,7 @@ protected function getVariationsRequest($getVariationsRequest)
             $httpBody = $_tempBody;
             // \stdClass has no __toString(), so we should encode it manually
             if ($httpBody instanceof \stdClass && $headers['Content-Type'] === 'application/json') {
-                $httpBody = \GuzzleHttp\json_encode($httpBody);
+                $httpBody = \GuzzleHttp\Utils::jsonEncode($httpBody);
             }
         } elseif (count($formParams) > 0) {
             if ($multipart) {
@@ -980,11 +980,11 @@ protected function getVariationsRequest($getVariationsRequest)
                 $httpBody = new MultipartStream($multipartContents);
 
             } elseif ($headers['Content-Type'] === 'application/json') {
-                $httpBody = \GuzzleHttp\json_encode($formParams);
+                $httpBody = \GuzzleHttp\Utils::jsonEncode($formParams);
 
             } else {
                 // for HTTP post (form)
-                $httpBody = \GuzzleHttp\Psr7\build_query($formParams);
+                $httpBody = \GuzzleHttp\Psr7\Query::build($formParams);
             }
         }
 
@@ -1002,7 +1002,7 @@ protected function getVariationsRequest($getVariationsRequest)
             $headers
         );
 
-        $query = \GuzzleHttp\Psr7\build_query($queryParams);
+        $query = \GuzzleHttp\Psr7\Query::build($queryParams);
         return new Request(
             'POST',
             $this->config->getHost() . $resourcePath . ($query ? "?{$query}" : ''),
@@ -1143,7 +1143,7 @@ public function searchItemsWithHttpInfo($searchItemsRequest)
     /**
      * Operation searchItemsAsync
      *
-     * 
+     *
      *
      * @param  \Amazon\ProductAdvertisingAPI\v1\com\amazon\paapi5\v1\SearchItemsRequest $searchItemsRequest SearchItemsRequest (required)
      *
@@ -1163,7 +1163,7 @@ function ($response) {
     /**
      * Operation searchItemsAsyncWithHttpInfo
      *
-     * 
+     *
      *
      * @param  \Amazon\ProductAdvertisingAPI\v1\com\amazon\paapi5\v1\SearchItemsRequest $searchItemsRequest SearchItemsRequest (required)
      *
@@ -1277,7 +1277,7 @@ protected function searchItemsRequest($searchItemsRequest)
             $httpBody = $_tempBody;
             // \stdClass has no __toString(), so we should encode it manually
             if ($httpBody instanceof \stdClass && $headers['Content-Type'] === 'application/json') {
-                $httpBody = \GuzzleHttp\json_encode($httpBody);
+                $httpBody = \GuzzleHttp\Utils::jsonEncode($httpBody);
             }
         } elseif (count($formParams) > 0) {
             if ($multipart) {
@@ -1292,11 +1292,11 @@ protected function searchItemsRequest($searchItemsRequest)
                 $httpBody = new MultipartStream($multipartContents);
 
             } elseif ($headers['Content-Type'] === 'application/json') {
-                $httpBody = \GuzzleHttp\json_encode($formParams);
+                $httpBody = \GuzzleHttp\Utils::jsonEncode($formParams);
 
             } else {
                 // for HTTP post (form)
-                $httpBody = \GuzzleHttp\Psr7\build_query($formParams);
+                $httpBody = \GuzzleHttp\Psr7\Query::build($formParams);
             }
         }
 
@@ -1314,7 +1314,7 @@ protected function searchItemsRequest($searchItemsRequest)
             $headers
         );
 
-        $query = \GuzzleHttp\Psr7\build_query($queryParams);
+        $query = \GuzzleHttp\Psr7\Query::build($queryParams);
         return new Request(
             'POST',
             $this->config->getHost() . $resourcePath . ($query ? "?{$query}" : ''),