diff --git a/CHANGELOG.md b/CHANGELOG.md
index b907a200..292713b0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Change Log
 
+## [4.66.6](https://github.com/plivo/plivo-php/tree/v4.66.6) (2025-03-14)
+**Enhancement - Fix implicit nullable warning .**
+- Fix warnings related to implicit nullable declaration from PHP 8.4.
+
 ## [4.66.5](https://github.com/plivo/plivo-php/tree/v4.66.5) (2025-02-25)
 **Enhancement - Supporting parameter_name in WhatsApp Template .**
 - Supporting `parameter_name` in WhatsApp Template .
diff --git a/src/Plivo/Http/PlivoResponse.php b/src/Plivo/Http/PlivoResponse.php
index 613d2e41..fa0b62fe 100644
--- a/src/Plivo/Http/PlivoResponse.php
+++ b/src/Plivo/Http/PlivoResponse.php
@@ -53,7 +53,7 @@ class PlivoResponse
      * @param array|null      $headers The headers of the response
      */
     public function __construct(
-        PlivoRequest $request = null,
+        ?PlivoRequest $request = null,
         $httpStatusCode = null,
         $content = null,
         array $headers = [])
@@ -149,4 +149,4 @@ public function __toString()
     {
         return '[PlivoResponse] HTTP ' . $this->getStatusCode() . ' ' . $this->content;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Plivo/HttpClients/PlivoGuzzleHttpClient.php b/src/Plivo/HttpClients/PlivoGuzzleHttpClient.php
index f82d852b..266df23b 100644
--- a/src/Plivo/HttpClients/PlivoGuzzleHttpClient.php
+++ b/src/Plivo/HttpClients/PlivoGuzzleHttpClient.php
@@ -44,8 +44,8 @@ class PlivoGuzzleHttpClient implements PlivoHttpClientInterface
      * @internal param Client|null $Handler .
      */
     public function __construct(
-        Client $guzzleClient = null,
-        BasicAuth $basicAuth = null,
+        ?Client $guzzleClient = null,
+        ?BasicAuth $basicAuth = null,
         $proxyHost = null,
         $proxyPort = null,
         $proxyUsername = null,
@@ -141,4 +141,4 @@ public function send_request($url, $method, $body, $headers, $timeOut, $request)
 
         return new PlivoResponse($request, $httpStatusCode, $rawBody, $rawHeaders);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Plivo/Version.php b/src/Plivo/Version.php
index 2d4c41ec..185d784e 100644
--- a/src/Plivo/Version.php
+++ b/src/Plivo/Version.php
@@ -26,7 +26,7 @@ class Version
      * @const int PHP helper library patch number
      */
 
-    const PATCH = 5;
+    const PATCH = 6;
 
     /**
      * @return string