transientDocuments The API caller does not have the permission to execute this operation

Hi,

I recently created a developer account. I am using the API endpoints with Postman. Most of the things are working and I got access token. However, when I try to send an API call to transient documents endpoint or send for signing endpoint, I get the following response.

API :  https://api.na3.echosign.com/api/rest/v6/transientDocuments

{
"code": "PERMISSION_DENIED",
"message": "The API caller does not have the permission to execute this operation"
}