How to enable subscription product in paypal checkout SDK

I am trying to add subscription in paypal checkout and I am using paypal checkout SDK but this not working

$environment = new PayPalCheckoutSdkCoreSandboxEnvironment(PAYPAL_SANDBOX_CLIENT_ID, 
PAYPAL_SANDBOX_CLIENT_SECRET);
$client = new PayPalCheckoutSdkCorePayPalHttpClient($environment);

$request = new PayPalCheckoutSdkOrdersOrdersCreateRequest();
$request->prefer('return=representation');

$subscription = ['plan_id' => '23423432',
'start_time' => '2023-09-01T00:00:00Z', 
'quantity' => 1];

$request->body = [
"intent" => "CAPTURE",
"purchase_units" => [[
    "reference_id" => $orderInfo['id'],
    "amount" => [
    "value" => $orderInfo['total'],
    "currency_code" => "AUD"
    ],
    'subscription' => $subscription,
]],
    "application_context" => [
        "cancel_url" => FRONTEND_APP_URL."order-status/?pstatus=payment-declined&source=paypal",
        "return_url" => FRONTEND_APP_URL."order-status/?pstatus=payment-processing&source=paypal"
    ] 
];

But in paypal nothing showing related to subscription. Please let me know how i can fix that