#255 request.POST passing JSON data

[Su]

Hello,
I am using Grinder 3.11 and seeing an issue with request.POST. I hope you can help.

I need to pass image (jpeg, tif) file contents in the JSON body of a HTTP request.
The expected URL request is this:
POST http://localhost:33333/importimage
with JSON body:
{"FileData":"data:image/tiff;base64,<base64 encoded="" data="">}
I can print the JSON data but I am not sure how to pass when JSON data in the HTTP request.</base64>

Below is code snippet I'm trying, however request.POST returns bad request.

response = request.GET(url)
#request.GET is successful.

file = open(filePath, 'r')
data = Codecs.base64Encode(String(file.read()))
file.close()
data = "data:image/jpeg;base64," + data
data = "\"{\"FileData\":\"" + data + ",\"PageSplitting\":true}\""
#print data 
headers = [
        NVPair('Content-Type', 'application/json'),
        NVPair('Content-Type', 'charset=utf-8'),
        NVPair('dataType', 'json'),
    ]

#request.POST fails with bad request
response = request.POST(getCreateImportJobURL(result["SessionID"]), data, headers)
#this fails too
response = request.POST(getCreateImportJobURL(result["SessionID"]), data,  [NVPair("Content-type", "application/json"),])

Could you please provide some pointers to help with this issue?
Thank you,
Su