Validate xml data (coming from URL) with XSD file (stored in project directory)

I have a XML data coming from API response, before I process the data insertion I wanted to check the data integrity. So, needs to validate the XML data with the XML file located in my system. When I used the code below :

$xsdPath = DOCUMENT_ROOT."/filePath/ssoResponse_xmlFormat.xsd";

    $xml = new \DOMDocument();
    $val = $xml->loadXML($xmlData); //$xmlData is XML data passed through function argument.



    if (!$xml->schemaValidate($xsdPath)) {
        //$xml->schemaValidate($xsdPath);
        return $this->libxml_display_errors();
    }else {
        return true;
    } 

I'm getting an error as :

Fatal Error 4: Start tag expected, '<' not found on line 1

Error 1872: The document has no document element. on line -1

Working with Zend Framework 2..

Thanks in advance..