You could subscribe for ORDER_STATUS_CHANGED webhook and get updates when your client's order change status.
Webhook structure:
{
“type”: “ORDER_STATUS_CHANGED”,
“orderId”: “UUID”,
“externalOrderId”: “external-merchant-order-id”,
“orderStatus”: “REQUEST/PROCESSING/CHANGED/CONFIRMED/DECLINED/EXPIRED/REJECTED/ARREST”,
“createdAt”: “yyyy-mm-ddThh:mm:ssZ”
}