Subscriptions API - Compute

Subscriptions API - Compute

When trying to POST to " https://subscriptions.zoho.com/api/v1/subscriptions/compute", I get "{"code":1000,"message":"Internal Error"}" as the response. I've double checked all my code to make sure that I'm POSTing identical data compared to " https://subscriptions.zoho.com/app", but it doesn't seem to work for me still. Any idea how I can get this to work, or, could ZOHO developers add a compute section to the API so that we don't have to do all the prorata calculations manually?

Thanks, 
Edward