Can residual values be retrieved via the Shopware API?

Yes, here is an example call via the Shopware API. The "acrisVoucherValue" field describes the current residual value of the respective voucher code. The order history is stored in the "acrisVoucher" field. The UUID in the filter refers to the UUID of the Shopware promotion. GET /api/search/promotion

{
    "page": 1,
    "limit": 1,
    "total-count-mode": 1,
    "filter": [
        { "type": "equals", "field": "id", "value": "01946eeb49647a7b9403ad92db5b44af" }
    ],
    "associations": {
        "individualCodes": {
            "associations": {
                "acrisVoucherValue": { },
                "acrisVoucher": { }
            }
        }
    }
}