I've been using the Zoho Invoice API quite happily up until this point using Node.js/Restify for my requests.

I'm trying to send the following request to create an estimate and am receiving this in the body of my response.

Error : {"code":15,"message":"Internal Error"}

Request : 

URL : https://invoice.zoho.com/api/v3/estimates?authtoken=******&organization_id=******

Post Data : { JSONString: '{"status":"draft","billing_address":{"address":"123 Fake St.","city":"Fake Town","zip":"12345","state":"Fake York","country":"Canada","fax":""},"shipping_address":{"address":"123 Fake St.","city":"Fake Town","zip":"12345","state":"Fake York","country":"Canada","fax":""},"line_items":[{"quantity":1,"item_id":"511266000000049005"},{"item_id":"511266000000045037","quantity":1},{"item_id":"511266000000045069","quantity":1}],"account_id":"511266000000050029","customer_id":"511266000000050029","contact_persons":["511266000000051013"],"custom_fields":[{"index":1,"value":"4x367"}],"discount_amount":0,"discount":0}',

  send: true,

  ignore_auto_number_generation: false }

Any ideas on how I should try to solve this?