Need Help Setting Up SSL Certificate for RESTful Endpoint with Powershell

I'm trying to set up an SSL endpoint on my server (Windows Server 2012 R2) so that it can receive https POSTs from an external server. I am using a simple REST framework for Powershell called RestPS: https://github.com/jpsider/RestPS to listen on port 8089 and I have an SSL certificate that I'm trying to use but I am getting errors when I try to use it. I'm very much a novice with SSL certificates and need some help. When I run Start-RestPSListener in Powershell, I get these messages:

SSL Certificate deletion failed, Error: 2
The system cannot find the file specified.

SSL Certificate add failed, Error: 1312
A specified logon session does not exist. It may already have been terminated.

Starting: https:// Listener on Port: 8089

I'm not sure what those errors mean or if they matter. But something isn't right because when I try to POST from the...