fix: update directChannel field name

Author: PatryQHyper

src/Model/Request/DirectChannel.php

@@ -20,7 +20,7 @@ public function __construct(string $directChannel)
     public function toArray(): array
     {
         return [
-            'direct_channel' => $this->value,
+            'directChannel' => $this->value,
         ];
     }
 }