Google calendar api implemention troubles

I’ve been trying to implement the google calendar API into my website so the end-user can see easier when there’s an appointment already set up so they don’t have to go through the issue of getting the error message of there already being an appointment set up for that date and time, but, google’s being a bitch and their guide is as straight forward as a curvy road, so, someone for the love of god help me out cuz I genuinely have no idea what I’m doing wrong since its their code, the only thing that might be wrong is the credentials.json file but again, the own google tutorial is shite and doens’t say fuck all on how to get them.

Code:

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

if (php_sapi_name() != 'cli') {
    throw new Exception('This application must be run on the command line.');
}

/**
 * Returns an authorized API client.
 * @return Google_Client the authorized client object
 */
function getClient()
{
    $client = new Google_Client();
    $client->setApplicationName('Google Calendar API PHP Quickstart');
    $client->setScopes(Google_Service_Calendar::CALENDAR_READONLY);
    $client->setAuthConfig(__DIR__ . '/credentials.json');
    $client->setAccessType('offline');
    $client->setPrompt('select_account consent');

    // Load previously authorized token from a file, if it exists.
    // The file token.json stores the user's access and refresh tokens, and is
    // created automatically when the authorization flow completes for the first
    // time.
    $tokenPath = 'token.json';
    if (file_exists($tokenPath)) {
        $accessToken = json_decode(file_get_contents($tokenPath), true);
        $client->setAccessToken($accessToken);
    }

    // If there is no previous token or it's expired.
    if ($client->isAccessTokenExpired()) {
        // Refresh the token if possible, else fetch a new one.
        if ($client->getRefreshToken()) {
            $client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
        } else {
            // Request authorization from the user.
            $authUrl = $client->createAuthUrl();
            printf("Open the following link in your browser:n%sn", $authUrl);
            print 'Enter verification code: ';
            $authCode = trim(fgets(STDIN));

            // Exchange authorization code for an access token.
            $accessToken = $client->fetchAccessTokenWithAuthCode($authCode);
            $client->setAccessToken($accessToken);

            // Check to see if there was an error.
            if (array_key_exists('error', $accessToken)) {
                throw new Exception(join(', ', $accessToken));
            }
        }
        // Save the token to a file.
        if (!file_exists(dirname($tokenPath))) {
            mkdir(dirname($tokenPath), 0700, true);
        }
        file_put_contents($tokenPath, json_encode($client->getAccessToken()));
    }
    return $client;
}


// Get the API client and construct the service object.
$client = getClient();
$service = new Google_Service_Calendar($client);

// Print the next 10 events on the user's calendar.
$calendarId = 'primary';
$optParams = array(
  'maxResults' => 10,
  'orderBy' => 'startTime',
  'singleEvents' => true,
  'timeMin' => date('c'),
);
$results = $service->events->listEvents($calendarId, $optParams);
$events = $results->getItems();

if (empty($events)) {
    print "No upcoming events found.n";
} else {
    print "Upcoming events:n";
    foreach ($events as $event) {
        $start = $event->start->dateTime;
        if (empty($start)) {
            $start = $event->start->date;
        }
        printf("%s (%s)n", $event->getSummary(), $start);
    }
}?>

Thanks in advance

Error given:
PHP Fatal error: Uncaught InvalidArgumentException: missing the required redirect URI in C:xampphtdocsprogramationsPAPIsrcuserStuffvendorgoogleauthsrcOAuth2.php:637
Stack trace:
#0 C:xampphtdocsprogramationsPAPIsrcuserStuffvendorgoogleapiclientsrcGoogleClient.php(328): GoogleAuthOAuth2->buildFullAuthorizationUri(Array)
#1 C:xampphtdocsprogramationsPAPIsrcuserStuffquickstart.php(38): Google_Client->createAuthUrl()
#2 C:xampphtdocsprogramationsPAPIsrcuserStuffquickstart.php(63): getClient()
#3 {main}
thrown in C:xampphtdocsprogramationsPAPIsrcuserStuffvendorgoogleauthsrcOAuth2.php on line 637

Fatal error: Uncaught InvalidArgumentException: missing the required redirect URI in C:xampphtdocsprogramationsPAPIsrcuserStuffvendorgoogleauthsrcOAuth2.php:637
Stack trace:
#0 C:xampphtdocsprogramationsPAPIsrcuserStuffvendorgoogleapiclientsrcGoogleClient.php(328): GoogleAuthOAuth2->buildFullAuthorizationUri(Array)
#1 C:xampphtdocsprogramationsPAPIsrcuserStuffquickstart.php(38): Google_Client->createAuthUrl()
#2 C:xampphtdocsprogramationsPAPIsrcuserStuffquickstart.php(63): getClient()
#3 {main}
thrown in C:xampphtdocsprogramationsPAPIsrcuserStuffvendorgoogleauthsrcOAuth2.php on line 637