"Box Sign request returns a 500 error."

I encountered a 500 error while using Postman to call the Box Sign API to create a sign request:

Endpoint:
https://api.box.com/2.0/sign_requests

Details:
The same developer token successfully works for file uploads. The application is approved and authorized.

Could you help identify the possible reasons for the issue?

{
    "type": "error",
    "code": "internal_server_error",
    "status": 500,
    "message": "Internal Server Error",
    "help_url": "https://developer.box.com/guides/api-calls/permissions-and-errors/common-errors/",
    "request_id": "0301ec73ba5420dac2e91dc81cc5f2845"
}