Sure - here is an example I just tried:
REQUEST
POST https://api.freeagent.com/v2/estimates HTTP/1.1
Accept-Encoding: gzip,deflate
User-Agent: QVSource (gzip)
QVSource: true
Authorization: Bearer XXXXXXXXXXX
Accept: application/xml
Content-Type: application/json
Host: api.freeagent.com
Content-Length: 318
Expect: 100-continue
{ estimate:{contact:
“https://api.freeagent.com/v2/contacts/1188344",dated_on:“2013-2-04T00:00:00+00:00”,currency:“USD”,exchange_rate:"1.0”,estimate_type:
“Quote”,status:“Draft”,notes: “Here are some
notes”,estimate_items:[{item_type: “Products”,description:“My
App”,price:“100”,quantity:“1”,category:“009” }] }}
RESPONSE
HTTP/1.1 500 Internal Server Error
Server: nginx/1.0.14
Content-Type: text/html; charset=utf-8
Connection: keep-alive
Status: 500 Internal Server Error
X-Runtime: 0.548472
X-Rev: 22bf745
X-Host: web3
Content-Length: 216