Authentication error when trying to write file to GCS, but no issue with read

[azraipoet]

Here is my config :

      'gcs' => [
        'driver' => 'gcs',
        'key_file_path' => storage_path().env('GOOGLE_CLOUD_KEY_FILE', null), // optional: /path/to/service-account.json
        'key_file' => [], // optional: Array of data that substitutes the .json file (see below)
        'project_id' => env('GOOGLE_CLOUD_PROJECT_ID', 'your-project-id'), // optional: is included in key file
        'bucket' => env('GOOGLE_CLOUD_STORAGE_BUCKET', 'your-bucket'),
        'path_prefix' => env('GOOGLE_CLOUD_STORAGE_PATH_PREFIX', ''), // optional: /default/path/to/apply/in/bucket
        'apiEndpoint' => env('GOOGLE_CLOUD_STORAGE_API_URI', null), // see: Public URLs below
        'visibility' => PortableVisibilityHandler::NO_PREDEFINED_VISIBILITY,
        'metadata' => ['cacheControl'=> 'public,max-age=86400'], // optional: default metadata
        'throw' => true,
    ],

This is my code to upload file to GCS :

      if($request->hasFile('logo')){
            $file = $request->file('logo');
            $extension = $file->getClientOriginalExtension();
            $storage = Storage::disk('gcs');
            $path = "logos/$org->id/logo.$extension";
            $storage->put($path, file_get_contents($file));
        }

Here's the error when it's trying to upload the file to GCS :
"message": "Unable to write file at location: logos/52/logo.jpeg. InvalidAuthenticationThe provided authentication header is invalid.Cannot use OAuth Authorization header with form POST.",

I have checked the permissions are all ok, my bucket is set to private. Is there anything that I have missed?