Bulk Update Records using REST API

I've been trying to bulk update records, using the REST API. However, while updating individual records works, the bulk update endpoint returns a 500 Internal Server Error.

I think I've followed the documentation by creating a Postman request like this (with the appropriate Authorization and Account-Id headers as tested with other requests):

PATCH https://app.smartsuite.com/api/v1/applications/{{app_id}}/records/bulk/
{
    "items": [
        {
            "title": "Service Levels",
            "status": {
                "value": "complete"
            }
        },
        {
            "title": "Load Balancers",
            "status": {
                "value": "complete"
            }
        }
    ]
}

The response body looks like this:

<!doctype html>
<html lang="en">

<head>
	<title>Server Error (500)</title>
</head>

<body>
	<h1>Server Error (500)</h1>
	<p></p>
</body>

</html>

The following request works (using the appropriate record ID instead of the placeholder):

PATCH https://app.smartsuite.com/api/v1/applications/{{app_id}}/records/[record-id]/
{
    "status": {
        "value": "ready_for_review"
    }
}