Modify other fields failed while doing transition

[Kaiwei Yang]

I see the document that I can modify other field such as title while doing transition.

https://developer.atlassian.com/cloud/jira/platform/rest/#api-api-2-issue-issueIdOrKey-transitions-post

This is my request body ,

{
 "update": {
 "summary": [
   {
     "set": "Bug sc"
   }
  ]
 },
 "fields": {
   "assignee": {
     "name": "xxxxx"
   }
 },
 "transition": {
   "id": "41"
 }
}

 This is response : { "errorMessages": [], "errors": { "summary": "Field 'summary' cannot be set. It is not on the appropriate screen, or unknown.", "assignee": "Field 'assignee' cannot be set. It is not on the appropriate screen, or unknown." } } Did I do something wrong ?