Laravel validate json data from payload

I'm wondering how I validate my json data in Laravel.

I have my data like this

In the controller I request like this

request('payment')['cardnumber']

How do I validate this.

Currently I have a RequestValidator class like this

public function rules()
    {
        return [
            'billing_address' => 'required',
            'town' => 'required',
            'county' => 'required',
        ];
    }

This is my controller

public function ProcessAdvertPayment(Property $property, Request $request, PropertyPaymentRequest $propertyPaymentRequest)
{

    $payload = $request->input('payload', false);
    $nonce = $payload['nonce'];

    $payment = Braintree_Transaction::sale([
        'amount' => 1,
        'paymentMethodNonce' => $nonce,
        'creditCard' => ['number' => request('payment')['cardnumber'], 'expirationDate' => request('payment')['month'] . '/' . request('payment')['year'], "cvv" => request('payment')['cvv']],
    ]);

    if($payment->success)
    {
        $property->payment()->create(['amount' => $payment->transaction->amount, 'braintree_transaction_id' => $payment->transaction->id, 'billing_address' => request('payment')['billing_address'], 'town' => request('payment')['town'], 'county' => request('payment')['county']]);
        return response()->json($payment);
    } 

    return response()->json(['error' => 'Payment Failed. Please try again or contact your payment provider for further help.'], 400);
}

via Chebli Mohamed