404 Error when Using Box Sign API

I am currently developing an application using the Box Sign API and encountering a persistent 404 Not Found error when attempting to create a sign request. Here are the details of the issue:

1. API Endpoint:
   • URL: https://api.box.com/2.0/sign_requests
   • HTTP Method: POST
2. Access Token: Full-authorization

1. Payload Sent:

{
    "signers": [
        {
            "role": "signer",
            "email": "<personal email-redacted>"
        }
    ],
    "source_files": [
        {
            "type": "file",
            "id": "1611107706949"
        }
    ],
    "parent_folder": {
        "type": "folder",
        "id": "278098710623"
    },
    "is_document_preparation_needed": true
}

5. Response Received:

{
    "type": "error",
    "code": "not_found",
    "status": 404,
    "message": "Not found",
    "help_url": "https://developer.box.com/guides/api-calls/permissions-and-errors/common-errors/",
    "request_id": "0e33bee75ee29cf32c3c2aefc0b0b7adb",
    "context_info": {
        "errors": [
            {
                "name": "Not Found",
                "message": "Not Found",
                "reason": "not_found"
            }
        ]
    }
}

6. Steps Taken:
   • Verified the existence and accessibility of the file and parent folder.
   • Confirmed that the access token has the necessary permissions and scopes.
   • Ensured the user associated with the access token has collaborator access to the file and folder.

Despite these steps, the error persists. Could you please help me identify any additional requirements or configurations needed to successfully create a sign request using the Box Sign API?