I am working on a proof of concept integrating the use of Zoho CRM as a data source for a front end app development platform.  I am able to authenticate with OAUTH just fine, and to use GET requests to pull in data from Zoho CRM.  However, all UPDATE and DELETE operations fail with a 400 BAD REQUEST error (I have not actually tried PUT yet, but I am betting it's the same).

I have copied the exact JSON body of the request, the exact endpoint, and the exact access token used when getting 400 errors into PostMan, and requests complete successfully that way.  The request from my app is being routed through a proxy server for compatibility with cross domain requests - this is my best guess as to what is causing the problem, but I can't work out why that would be causing a problem.  If anyone has thoughts on what could be the cause, or troubleshooting steps to try I would appreciate it.