Cannot get OAuth credentials be recognized by PHP script

[M T]

Hello,
Im trying to write a PHP script to check historical data of avg monthly 
searches for a given keywords list. However I cannot get the credential 
files to work.

// planner.php
use Google\Ads\GoogleAds\Lib\V18\GoogleAdsClientBuilder;
use Google\Ads\GoogleAds\V18\Services\
GenerateKeywordHistoricalMetricsRequest;

require 'vendor/autoload.php';

$configFilePath = 'google_ads_php.ini';

$googleAdsClient = (new GoogleAdsClientBuilder())
    ->fromFile($configFilePath)
    ->build();

$customerId = '9810123038'; 

try {
    $keywordPlanService = $googleAdsClient->getKeywordPlanIdeaServiceClient
();
    $keywords = ['test keyword', 'another keyword'];

    $request = new GenerateKeywordHistoricalMetricsRequest([
        'keywords' => $keywords
    ]);

    $response = $keywordPlanService->generateKeywordHistoricalMetrics(
$request);

    foreach ($response->getMetrics() as $metric) {
        printf(
            "Keyword: %s, Avg monthly volume: %d\n",
            $metric->getText(),
            $metric->getMetrics()->getAvgMonthlySearches()
        );
    }
} catch (Exception $e) {
    printf("Error: %s\n", $e->getMessage());
}

in the same folder as code above I have 2 files:
// google_ads_php.ini

[GOOGLE_ADS]
developerToken = "cut"
jsonKeyFilePath = "E:/path/to/credentials.json"
scopes = "https://www.googleapis.com/auth/adwords";
clientId = "clientid.apps.googleusercontent.com"
clientSecret = "cut"
refreshToken = "cut"
Ive got the refreshToken from buildFullAuthorizationUri() that prompted 
google login screen correctly.
and:
// credentials.json

{"web":
{"client_id":"cut",
"project_id":"cut",
"auth_uri":"https://accounts.google.com/o/oauth2/auth";,
"token_uri":"https://oauth2.googleapis.com/token";,
"auth_provider_x509_cert_url":"https://www.googleapis.com/oauth2/v1/certs";,
"client_secret":"cut",
"redirect_uris":["http://localhost"]}}

No matter what I do I cannot go over:
*Fatal error*: Uncaught InvalidArgumentException: OAuth2 authentication 
credentials must not be null. 
Stack trace: #0
Google\Ads\GoogleAds\Lib\V18\GoogleAdsClientBuilder->validate() 
Google\Ads\GoogleAds\Lib\V18\GoogleAdsClientBuilder->build()
thrown in  
*google-ads-php\src\Google\Ads\GoogleAds\Lib\V18\GoogleAdsClientBuilder.php*
 on line *429* 

Any ideas on how to solve that? File paths are correct because I can print 
those files content. 

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