Can't able to invoke the FND_USER_PKG using REST service

Hi Team,

I am trying to invoke this package(FND_USER_PKG) using REST service but it is showing the following error.

{

"ISGServiceFault": {

"Code": "ISG_SERVICE_EXECUTION_ERROR",

"Message": "Error occurred while executing the web service request",

"Resolution": "System error, please see service log trace for details.",

"ServiceDetails": {

"ServiceName": "FndUsrPkg",

"OperationName": "testusername",

"InstanceId": "0"

}

}

}

kindly help me for same.

Note: I have attached the issue log for reference.

Regards,

krishna