Laravel Array from Paypal Rest API

Hi.

Im struggling to get the data out of the Returned data from Paypal Api..

When a payment is made all is ok and If i call ::

$payment = Payment::get($payment_id, $this->_api_context)->toArray();

return $payment; // for testing all data returned
return $payment['transactions']['related_resources']['transaction_fee']; // trying to get the data

I get

{
   "id": "PAY-2VF66335NA......",
   "intent": "sale",
   "state": "approved",
   "cart": "7JA26864N.../.",
   "payer": {
      "payment_method": "paypal",
      "status": "VERIFIED",
      "payer_info": {
         "email": "test@my_app.co.uk",
         "first_name": "Chris",
         "last_name": "",
         "payer_id": "T26U6W.....",
         "shipping_address": {
            "recipient_name": "Chris",
            "line1": "Spitalfields Arts Market, 112 Brick Lane,",
            "city": "London",
            "state": "London",
            "postal_code": "E1 6RL",
            "country_code": "GB"
         },
         "country_code": "GB"
      }
   },
   "transactions": [
      {
         "amount": {
            "total": "10.00",
            "currency": "GBP",
            "details": {}
         },
         "payee": {
            "merchant_id": "25NU22K....",
            "email": "[email protected]"
         },
         "description": "Mailbox Topup",
         "item_list": {
            "items": [
               {
                  "name": "Mailbox Topup",
                  "price": "10.00",
                  "currency": "GBP",
                  "quantity": 1
               }
            ],
            "shipping_address": {
               "recipient_name": "Chris",
               "line1": "Spitalfields Arts Market, 112 Brick Lane,",
               "city": "London",
               "state": "London",
               "postal_code": "E1 6RL",
               "country_code": "GB"
            }
         },
         "related_resources": [
            {
               "sale": {
                  "id": "5SK92059H7....",
                  "state": "pending",
                  "amount": {
                     "total": "10.00",
                     "currency": "GBP",
                     "details": {
                        "subtotal": "10.00"
                     }
                  },
                  "payment_mode": "INSTANT_TRANSFER",
                  "reason_code": "PAYMENT_REVIEW",
                  "protection_eligibility": "INELIGIBLE",
                  "transaction_fee": {
                     "value": "0.54",
                     "currency": "GBP"
                  },
                  "parent_payment": "PAY-",
                  "create_time": "2018-11-26T13:24:26Z",
                  "update_time": "2018-11-26T13:24:26Z",
                  "links": [
                     {
                        "href": "https://api.sandbox.paypal.com/v1/payments/sale/",
                        "rel": "self",
                        "method": "GET"
                     },
                     {
                        "href": "https://api.sandbox.paypal.com/v1/payments/sale//refund",
                        "rel": "refund",
                        "method": "POST"
                     },
                     {
                        "href": "https://api.sandbox.paypal.com/v1/payments/payment/",
                        "rel": "parent_payment",
                        "method": "GET"
                     }
                  ],
                  "soft_descriptor": "PAYPAL *TESTFACILIT"
               }
            }
         ]
      }
   ],
   "redirect_urls": {
      "return_url": "https://my-app.test/payments/paypal/status?",
      "cancel_url": "https://my-app.test/payments/paypal/status"
   },
   "create_time": "2018-11-26T13:24:26Z",
   "update_time": "2018-11-26T13:24:25Z",
   "links": [
      {
         "href": "https://api.sandbox.paypal.com/v1/payments/payment/",
         "rel": "self",
         "method": "GET"
      }
   ]
}

But when I try accessing the Transaction Fee I get an error Undefined index: related_resources.

How do i get that data?

Many thansk