schannel error are Windows are typically due to using https and self-signed certificates or certificates that cannot be checked for revocation.
HTTP Request, which uses libcurl dynamically links to WinSSPI which is the certificate "vault" for the OS. Any certificate that is installed locally cannot be verified.
curl that Craige mentions automatically turns verification off, which while it works, will defeat the use of https. That is, the connection will still be encrypted, but the certificate used to encrypt it is unverified. In short, you have to know you trust it.
HTTP Request allows you to turn secure off, using Secure(0)
Additionally,
JMP 16 introduced:
Certificates( "c:\certs\my_certificate.crt" );
which will allow you to use your own certificate file
and
Verify SSL( "false" )
which will turn certificate verification off.