For Billflow to know which product belongs to your service you must utilize metadata tags. Every product that corresponds to your service's particular plan must be tagged with the same ''sb_service" tag. In addition, each of these products will have a unique "sb_tier" that corresponds to the particular price of that tier. The "sb_service" tag encapsulates all of the products that you created for a particular plan. This is what "glues" the products together. The "sb_tier" tag is what differentiates one product from the next in your plan. As such, it is important that your "sb_service" tag do not change within the plan. And your "sb_tier" tags change with the tier that you create.