Unable to run example code

[trueandperfect]

Fatal error: Uncaught Error: Class "GlobalPayments\Api\ServiceConfigs\Gateways\GpApiConfig" not found in /workspace/GenerateToken.php:19 Stack trace: #0 /workspace/GenerateToken.php(32): GenerateToken->__construct() #1 /workspace/index.php(8): GenerateToken::getInstance() #2 {main} thrown in /workspace/GenerateToken.php on line 19

I have deployed the sample code gp-api. Not sure what I am missing here.

[trueandperfect]

Now I am getting the following error:
File not found.

/*
 * Document details
 * 
 * var GlobalPayments\Api\Entities\PayFac\UploadDocumentData
 */
public function withUploadDocumentData($uploadDocumentData)
{
    //file validations
    if (!file_exists($uploadDocumentData->documentLocation)) {
        throw new BuilderException('File not found!');
    } elseif (filesize($uploadDocumentData->documentLocation) > 5000000) {
        throw new BuilderException('Max file size 5MB exceeded');
    }