Refresh token must be passed in or set as part of setAccessToken Youtube API

Question

I have the following code

if (file_exists($credentialsPath)) {

    $accessToken = file_get_contents($credentialsPath);

    $client->setAccessToken($accessToken);

    if ($client->isAccessTokenExpired()) {
        $client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
        $newAccessToken = $client->getAccessToken();
        $accessToken = array_merge($accessToken, $newAccessToken);
        file_put_contents($credentialsPath, json_encode($accessToken));
    }
} 

But after an hour, if I try to use Youtube Data API, I am getting the following error,

Fatal error: Uncaught exception 'LogicException' with message 'refresh token must be passed in or set as part of setAccessToken' in /var/sentora/hostdata/zadmin/public_html/classes/library/youtube/vendor/google/apiclient/src/Google/Client.php:267 Stack trace: #0 /var/sentora/hostdata/zadmin/public_html/classes/library/youtube/youtube.php(26): Google_Client->fetchAccessTokenWithRefreshToken(NULL) #1 /var/sentora/hostdata/zadmin/public_html/channel/apiwrap.php(3): require_once('/var/sentora/ho...') #2 {main} thrown in /var/sentora/hostdata/zadmin/public_html/classes/library/youtube/vendor/google/apiclient/src/Google/Client.php on line 267

Please help.