Why repeater data does not included in mutateFormDataBeforeCreate() function?

Undefined array key "item_variations"

<?php
class CreateInvoice extends CreateRecord
{
    protected static string $resource = InvoiceResource::class;
    protected function mutateFormDataBeforeCreate(array $data): array
    {
        \Midtrans\Config::$serverKey = config('midtrans.serverKey');
        \Midtrans\Config::$isProduction = false;
        \Midtrans\Config::$isSanitized = true;
        \Midtrans\Config::$is3ds = true;
        $repeater = $data['item_variations'];
        $totalPrice = 0;
        for ($i=0; $i < count($repeater); $i++) { 
            $totalPrice += $repeater[$i]['price'];
        }
        $partner = Partner::find($data['partner_id']);

        $params = array(
            'transaction_details' => array(
                'order_id' =>  rand(),
                'gross_amount' => $totalPrice,
            ),
            'customer_details' => array(
                'first_name' => $partner->name,
                'phone' => $partner->phone_number,
            ),
        );

        $snapToken = \Midtrans\Snap::getSnapToken($params);
        $data['midtrans_order_id'] = $snapToken;
    
        return $data;
    }
}