Swish API Testing

I am testing swish payment gateway of swish. whenever i make a call from my xampp server it give me error like Fatal error: Curl failed with error #58: unable to use client certificate (no key found or wrong pass phrase?) in /opt/lampp/htdocs/getswish-api-master/ajax.php on line 192 kindly help me out. P.S I am using this API

Swish API Github