Error while creating Oracle BIP report using REST

 am new to Rest API and Oracle BIP. I am tryin to create simple report using rest API but getting some errors. I have set authentication and user agent correctly.

I am getting response as Status_code: 500 Reason_phrase - Internal Server Error The response is in soap format and the fault string is as below ns1:Client.NoSOAPAction no SOAPAction header! I am not sure what this MyReportRequest is as this was mentioned in Oracle doc.I copied it as it is. Below is my code snippet. I am not sure if request_url is correct?

input_json := '{"absolutePath": "' || '/myCustompath/' || '",
"dataModelPath": "' || '/myCustompath/test.xdm' || '",
"name": "' || 'testreport' || '",
"update": "' ||'true'|| '"
}'; 
request_url:='https://testhostname/xmlpserver/services
/PublicReportService_v11/rest/v1/createReport';
http_variable_Req:= utl_http.begin_request(request_url,'POST','HTTP/1.1');
utl_http.set_header(http_variable_Req, 'content-type', 
'application/json');
utl_http.set_header(http_variable_Req, 'Content-Disposition', 'Content- 
Disposition: form-data; name="MyReportRequest"');