Hello Veera,
Are you sure that robot exists and it's up and running?
In the machine are you using the old Robot agent or are you using the UiPath Agent Desktop?
The start job JSON I use is slightly different. I use;
{ "startInfo": { "ReleaseKey": "120f3a6b-bbbb-aaaa-b3e2-83769b513ac9", "Strategy": "Specific", "RobotIds": [ 999999 ], "NoOfRobots": 0, "Source": "Manual", "InputArguments": "" } }
You can check the swagger for the service on your cloud using the following url:
https://cloud.uipath.com/<AccountName>/<TenantName>/orchestrator_/swagger/index.html#/Jobs/Jobs_StartJobs
Best regards,
Miguel Amado