Invalid Request OpenSSL Error: Adding a new site to MainWP on Windows

I have been setting up MainWP on Windows and I ran into an issue when trying to add my first site. MainWP’s dashboard gave me an error, “Invalid Request” – not very descriptive. When I looked in my PHP error log I found: “[10-Dec-2016 14:20:34 UTC] PHP Warning: openssl_pkey_get_details() expects parameter 1 to be resource, […]