Issue with Custom Guzzle Client in authenticationClient for SellingPartnerApi::seller()

I’m encountering an issue when passing a custom GuzzleHttpClient instance as the authenticationClient parameter in SellingPartnerApi::seller(). According to the documentation, this parameter should accept a GuzzleHttpClient, but when provided, it results in the following error:

Error:

Typed property SaloonHttpSendersGuzzleSender::$client must not be accessed before initialization.

Steps to Reproduce
Instantiate a GuzzleHttpClient with a proxy

$httpClient = new GuzzleHttpClient([
    'proxy' => 'http://username:password@proxy_host:port',
    'timeout' => 30,
    'connect_timeout' => 30,
]);
// or just an empty client
$httpClient = new GuzzleHttpClient();

Pass it to SellingPartnerApi::seller()

$api = SellingPartnerApi::seller(
    clientId: $credentials->api_client_id,
    clientSecret: $credentials->api_client_secret,
    refreshToken: $credentials->refresh_token,
    endpoint: Endpoint::NA,
    authenticationClient: $httpClient
);

Attempt to make a request:

$response = $api->sellersV1()->getMarketplaceParticipations();

Additional Information

• PHP: 8.4.1
• Selling Partner API SDK: 7.2.4 (jlevers/selling-partner-api)
• Guzzle: 7.9.2
• Laravel: 11.41.3

I’ve confirmed that the issue persists even when using a clean GuzzleHttpClient instance without additional configuration.

Is there an internal constraint preventing the use of a custom GuzzleHttpClient, or is there a required initialization step that is missing? Any guidance would be appreciated.