Unable to establish a Chat session

Summary:

Unable to establish a Chat session due to following error.

{

    "type": "https://rnowgse12015.rightnowdemo.com/services/rest/crossChannelServices/exceptions/OSC-CREST-00006",

    "title": "An attempt to write a resource failed",

    "status": 400,

    "detail": "A problem setting a property was encountered: not an object; EstablishSession.SessionInformation",

    "instance": "https://rnowgse12015.rightnowdemo.com/services/rest/crossChannelServices/latest/establishSessions",

    "o:errorCode": "OSC-CREST-00006"

}

Content (required):

URL: https://rnowgse12015.rightnowdemo.com/services/rest/crossChannelServices/latest/establishSessions

{

 "sessionInformation": {

 "emailAddress" : "[email protected]", 

 "firstName" : "NG",

 "lastName": "Customer", 

 "question" : "Refunds Issues"

  }

 }

https://docs.oracle.com/en/cloud/saas/service/19a/cxscc/c_chat_establish_sessions.html

Version (include the version you are using, if applicable):