Unable to update Description of an issue through API

[CHINNAMUTHEVISAI.SATYANARAYANASHARMA]

Hi ,

I'm trying to update issue description using Postmen .
I'm getting this error 

Operation value must be an Atlassian Document (see the Atlassian Document Format)

I'm passing these values

put {{Base url}}/rest/api/3/issue/:STPS-100

Header : 

content-type : application/json 

body : 

{

  "fields": {

    "description":"Variable Test in Postme"

  }

}

i'm able to edit Summary , but not able to change it for Desciption.

please help

[CHINNAMUTHEVISAI.SATYANARAYANASHARMA]

How do i close this request , as i able to execute it now.