ApplePay Integration Using Amazon Payment Services

I am a web developer trying to integrate ApplePay into a WooCommerce website using the Amazon Payment Services plugin. I followed the documentation provided by the plugin authors multiple times on two different servers, however, every time I try to test my integration I get the following error:

cURL error 60: SSL certificate problem: unable to get local issuer certificate.

I would like to find someone who can help me debug and fix this issue in a timely manner.