How can GPSR product information be updated via the API?

The plugin saves the GPSR information on the additional fields on the product. Here is an example call of the Sync API on the product:

{
    "key": "write",
    "action": "upsert",
    "entity": "product",
    "payload": [
        {
            "id": "2a88d9b59d474c7e869d8071649be43c",
            "customFields": {
                "acris_gpsr_product_type": "Product type and product identifiers",
                "acris_gpsr_product_manufacturer": "Manufacturer information",
                "acris_gpsr_product_contact": "Responsible person (EU)",
                "acris_gpsr_product_hint_warning": "Warning note",
                "acris_gpsr_product_hint_safety": "Safety note",
                "acris_gpsr_product_hint_information": "Important information"
            },
            "acrisGpsrDownloads": [
                {
                    "mediaId": "0198552916a47a52a355375995611bdb",
                    "gpsrType": "warning_note"
                },
                {
                    "mediaId": "0198552916a47a52a355375995611bdb",
                    "gpsrType": "security_note"
                },
                {
                    "mediaId": "0198552916a47a52a355375995611bdb",
                    "gpsrType": "important_info"
                }
            ]
        }
    ]
}