Grade point update using core_grades_update_grades function?

by prasad pulipati.  

How to update the grade points of the particular student? Can any one provide the url for curl test?

I tried this one

http://localhost/webservice/rest/server.php?wstoken=668e1da48055ba6e02f8f12&wsfunction=core_grades_update_grades&courseid=2&component=Col2&itemnumber=4&userid=1&finalgrade=100.0&feedback=well

I am getting following error

{"exception":"invalid_parameter_exception","errorcode":"invalidparameter","message":"Invalid parameter value detected","debuginfo":"Missing required key in single structure: source"}