Securing FM XML API requests

Hi, I've just upgraded to Filemaker Server 16 and installed an SSL certificate for client/server communications. However, I am confused by the documentation when it comes to communication between the Server and the Filemaker XML API. We're currently making these calls from another server over http, and would like to ensure they are secure.

I've attempted changing these requests to be over https but this seems to fail - I haven't investigated where exactly (if it's a limitation of the PyFilemaker Python library we're using or the fact that the connection is not actually secure).

Would enabling it for clients also provide security on the API side? Could anyone provide some guidance on where I can look for information on this?

Thanks in advance!