Issue with Completing Purchase Orders via Extended Endpoint in MYOB Advanced

Hi everyone,

I recently set up a new instance in MYOB Advanced and extended a new endpoint specifically for managing Purchase Orders. I'm trying to complete a purchase order through this endpoint, but I keep encountering an error. I'm hoping someone might be able to shed some light on this issue.

Endpoint and Request: I'm sending a POST request to:
POST http://localhost/MyStoreInstance7/entity/Default/1.1/PurchaseOrders/CompleteProcessingCategory

With the following JSON body:
{
  "entity": {
    "OrderNbr": "PO001326"
  }
}

Response: However, I'm receiving a 500 Internal Server Error with the following details:
{
    "message": "An error has occurred.",
    "exceptionMessage": "Operation failed",
    "exceptionType": "PX.Data.PXInvalidOperationException",
    "stackTrace": "...",
    "innerException": {
        "message": "An error has occurred.",
        "exceptionMessage": "The Complete Order button is disabled.",
        "exceptionType": "PX.Data.PXActionDisabledException",
        "stackTrace": "..."
    }
}

It seems that the "Complete Order" button is disabled, but I'm not sure why this would be the case, especially since the button is not disabled when I check in the MYOB Advanced UI and API user has access. Has anyone encountered a similar issue or have any suggestions on how to resolve this? Any insights or advice would be greatly appreciated.

Thank you in advance!