Access Google My Business Statistics with API in php - php

Question

I manage approximately 200 Google My business accounts, all being owned under an email XXX#YYY.com
I would like to use the Google My Business API using a PHP SDK to retrieve all types of stats regarding each accounts (ie. view per timeframe, view through map, view through SERP, etc...).
I did get the authorization to use the Google My Business API and I downloaded the php SDK: https://developers.google.com/my-business/samples/google-api-services-mybusiness-v4p9-php-rev-20210224-1.zip?hl=fr
I also created a service account (which I'm really not familiar with) in order to auth with the library.
Now here is my code :
$client = new Google_Client();
$client->useApplicationDefaultCredentials();
// set the service account json file location manually
$client->setAuthConfig(__DIR__.'/../global/yyyyy-xxxx-xxxxxxxxxx.json');
$client->setApplicationName("yyyyyb");
// set the scope to access GMBs
$client->setScopes([
"https://www.googleapis.com/auth/business.manage"
]);
$this->client = $client;
$mybusinessService = new Google_Service_Mybusiness($client);
$accounts = $mybusinessService->accounts;
$accountsList = $accounts->listAccounts()->getAccounts();
echo "<pre>";
print_r($accountsList);
echo "</pre>";
$locationNames = array("Paris");
$insightReqObj = new Google_Service_MyBusiness_ReportLocationInsightsRequest();
$insightReqObj->setLocationNames($locationNames);
$basicReqObj = new Google_Service_MyBusiness_BasicMetricsRequest();
// datetime range is mandatory
// TODO :: validate to not allow more than 18 months difference
$timeRangObj = new Google_Service_MyBusiness_TimeRange();
$timeRangObj->setStartTime("2020-01-01T15:01:23Z");
$timeRangObj->setEndTime("2021-01-11T15:01:23Z");
$metricReqObj = new Google_Service_MyBusiness_MetricRequest();
$metricReqObj->setMetric('ALL');
$basicReqObj->setMetricRequests(array($metricReqObj));
$basicReqObj->setTimeRange($timeRangObj);
$insightReqObj->setBasicRequest($basicReqObj);
$allInsights = $mybusinessService->accounts_locations->reportInsights("accounts/XXXXXXXX",$insightReqObj);
echo "<pre>";
print_r($allInsights);
echo "</pre>";
There are two issues :
When I print the accountlist, I only find information about my service account, I was expecting a list of all the accounts managed by my email : XXX#YYY.com ; I realise that it makes no sense since I don't even know how to grant the service account access to the My Business account managed by this email.
Also AllInsignt generate an error :
How can I access the statistics of all the accounts managed by my Gmail account : XXX#YYY.com ?