Apple Pay - NSS error -8178

I'm integrating Apple pay to website in PHP, by following the tutorial in https://github.com/norfolkmustard/ApplePayJS . However I'm getting following error if I click the apple pay button.

unable to load client key: -8178 (SEC_ERROR_BAD_KEY)

When I checked the error in detail I'm getting below details:

enter image description here

I even tried disabling the SSL in curl by adding: curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

Any help would be appreciated, Thanks in advance.