This is a tough question. To get that signature sweet tangy flavor, some type of sugar is required. Commercial brands that advertise their product as "sugar-free" usually have some kind of sugar substitute such as stevia, allulose, or sucralose added (look at the ingredient list to make sure). The beauty of making your own sauce is that you can cut back on the added sugar. Simply use less. If you prefer more natural sugars, use maple syrup, honey, or puréed fruit.