diff --git a/.circleci/config.yml b/.circleci/config.yml
index 9d95795..ca3e285 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -12,7 +12,7 @@ jobs_default: &jobs_default
     php-version: << matrix.php-version >>
   matrix:
     parameters:
-      php-version: [ *php_min, "8.2", "8.3" ]
+      php-version: [ *php_min, "8.2", "8.3" , "8.4" ]
 
 jobs:
   cs-fixer:
diff --git a/composer.json b/composer.json
index 00fd016..9afe9a6 100644
--- a/composer.json
+++ b/composer.json
@@ -24,10 +24,10 @@
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^3.13",
-        "php-coveralls/php-coveralls": "2.5",
+        "php-coveralls/php-coveralls": "^2.7",
         "phpunit/phpunit": "^10.0",
-        "phpstan/phpstan": "^1.10",
-        "rector/rector": "^0.19.0"
+        "phpstan/phpstan": "^2.0",
+        "rector/rector": "^2.0"
     },
     "autoload": {
         "psr-0": {
diff --git a/src/Bigcommerce/Api/Client.php b/src/Bigcommerce/Api/Client.php
index e64100c..7f14a47 100644
--- a/src/Bigcommerce/Api/Client.php
+++ b/src/Bigcommerce/Api/Client.php
@@ -269,7 +269,7 @@ public static function getConnection()
      * @param Connection|null $connection The connection to use
      * @return void
      */
-    public static function setConnection(Connection $connection = null)
+    public static function setConnection(?Connection $connection = null)
     {
         self::$connection = $connection;
     }
diff --git a/src/Bigcommerce/Api/Connection.php b/src/Bigcommerce/Api/Connection.php
index 707acac..e1464f0 100644
--- a/src/Bigcommerce/Api/Connection.php
+++ b/src/Bigcommerce/Api/Connection.php
@@ -28,7 +28,7 @@ class Connection
     private $curl;
 
     /**
-     * @var array<string, string> Hash of HTTP request headers.
+     * @var array<int, string> Hash of HTTP request headers.
      */
     private $headers = [];
 
@@ -258,7 +258,7 @@ public function removeHeader($header)
     /**
      * Return the request headers
      *
-     * @return array<string, string>
+     * @return array<int, string>
      */
     public function getRequestHeaders()
     {