Using 'before' parameter when retrieving responses

I am attempting to use the ‘before’ query parameter to filter responses by date using Postman, but am being met with consistent 400 Bad Request responses, with the following body:

"code": "BAD_REQUEST",
    "description": "The provided value is invalid.",
    "details": [
        {
            "code": "INVALID_PARAMETER",
            "description": "value should be alphanumeric: before",
            "in": "QUERY",
            "field": "before"
        }
    ]

I have tried several iterations of the value for the ‘before’ parameter including:

2022-11-28T01:01:01Z
2022-11-28T01%3A01%3A01Z
2022-11-28T01:01:01
2022-11-28T01:01:01.001Z
2022-11-28T00:00:00Z

I am using URL: https://api.typeform.com/forms/{{form_id}}/responses?page_size=1000&before=2022-11-28T01:01:01Z

Am I missing some trick to this?