403 error while creating HR Helpdesk Sr using Rest API

Hi Team,

We are having a requirement to create HR Helpdesk service request using REST API call via OIC integration.

Am using below API for the same but receiving 403 forbidden error:

/crmRestApi/resources/11.13.18.05/hrHelpDeskRequests

Payload used-

{
"required": [
"BUOrgId",
"Title"
],
"type": "object",
"properties": {
"Title": {
"title": "Subject",
"maxLength": 400,
"type": "string",
"description": "The brief title of the service request.",
"nullable": false
}
}
}

Can someone help what would be the issue causing it?

Note: Is there any pre-requisites wrt user details used in authentication? We are not using any cred like ****@oracle.com instead it is customer email id.