//Two responses?..one from each request
$response = $service->findItemsAdvanced($request);

// how to get compatibles from item id in request/response 1 ?//
$response2 = $service-> /* ??? */  ($request2);


// Iterate over the items returned in the response.
foreach ($response->searchResult->item as $item) {
    //an easy var name for reference
    var mylistId = $item->itemId,
    // lets the see the ID's //
    printf(
        "(%s) %sn",
        $item->itemId,
        $item->title
    );

   //maybe the request and response is in the loop???
   // $requestTWO = get compatibles linked to mylistId
   // $responseTWO = return compatibles
   foreach ($responseTWO->searchResult->item as $compats) {
       // print new responses
       printf(
        "(%s) %sn",
        $compats->make,
        $compats->model,
        $compats->year
    );
}

<?php
require __DIR__.'/vendor/autoload.php';

use DTSeBaySDKSdk;
use DTSeBaySDKConstants;
use DTSeBaySDKFinding;
use DTSeBaySDKShopping;

$sdk = new Sdk([
    'credentials' => [
        'devId' => 'DEV ID',
        'appId' => 'APP ID',
        'certId' => 'CERT ID',
    ],
    'globalId'    => ConstantsGlobalIds::MOTORS
]);

/**
 * Create the service objects.
 */
$finding = $sdk->createFinding([
    'apiVersion' => '1.13.0'
]);

$shopping = $sdk->createShopping([
    'apiVersion' => '981'
]);

/**
 * Create the finding request.
 */
$findingRequest = new FindingTypesFindItemsAdvancedRequest();
/**
 * Ask for items from these sellers. You specify up to 100 sellers.
 */
$itemFilter = new FindingTypesItemFilter();
$itemFilter->name = 'Seller';
$itemFilter->value = [
    'brakemotive76',
    'primechoiceautoparts'
];
$findingRequest->itemFilter[] = $itemFilter;
/**
 * You can optionally narrow the search down further by only requesting
 * listings that match keywords or categories.
 */
//$request->keywords = 'Brake Pads';
//$request->categoryId = ['33560', '33561'];

/**
 * eBay can return more than one page of results.
 * So just start at page 1 to begin with.
 */
$findingRequest->paginationInput = new FindingTypesPaginationInput();
$pageNum = 1;

do {
    $findingRequest->paginationInput->pageNumber = $pageNum;

    $findingResponse = $finding->findItemsAdvanced($findingRequest);

    // Handle any errors returned from the API.
    if (isset($findingResponse->errorMessage)) {
        foreach ($findingResponse->errorMessage->error as $error) {
            printf(
                "%s: %snn",
                $error->severity=== FindingEnumsErrorSeverity::C_ERROR ? 'Error' : 'Warning',
                $error->message
            );
        }
    }

    if ($findingResponse->ack !== 'Failure') {
        /**
         * For each item make a second request to the Shopping service to get the compatibility information.
         */
        foreach ($findingResponse->searchResult->item as $item) {
            $shoppingRequest = new ShoppingTypesGetSingleItemRequestType();
            $shoppingRequest->ItemID = $item->itemId;
            /**
             * We have to tell the Shopping service to return the comaptibility and item specifics information as
             * it will not by default.
             */
            $shoppingRequest->IncludeSelector = 'ItemSpecifics, Compatibility';

            $shoppingResponse = $shopping->getSingleItem($shoppingRequest);

            if (isset($shoppingResponse->Errors)) {
                foreach ($shoppingResponse->Errors as $error) {
                    printf(
                        "%s: %sn%snn",
                        $error->SeverityCode === ShoppingEnumsSeverityCodeType::C_ERROR ? 'Error' : 'Warning',
                        $error->ShortMessage,
                        $error->LongMessage
                    );
                }
            }

            if ($shoppingResponse->Ack !== 'Failure') {
                $item = $shoppingResponse->Item;

                print("n$item->Titlen");

                if (isset($item->ItemSpecifics)) {
                    print("nThis item has the following item specifics:nn");
                    foreach ($item->ItemSpecifics->NameValueList as $nameValues) {
                        printf(
                           "%s: %sn",
                            $nameValues->Name,
                             implode(', ', iterator_to_array($nameValues->Value))
                        );
                    }
                }

                if (isset($item->ItemCompatibilityCount)) {
                    printf("nThis item is compatible with %s vehicles:nn", $item->ItemCompatibilityCount);

                    foreach ($item->ItemCompatibilityList->Compatibility as $compatibility) {
                        foreach ($compatibility->NameValueList as $nameValues) {
                            if ($nameValues->Name != '') {
                                printf(
                                    "%s: %sn",
                                    $nameValues->Name,
                                    implode(', ', iterator_to_array($nameValues->Value))
                                );
                            }
                        }
                        printf("Notes: %s n", $compatibility->CompatibilityNotes);
                    }
                }
            }
        }
    }

    $pageNum += 1;

} while ($pageNum <= $findingResponse->paginationOutput->totalPages);