ChargeItem needs a new element "product" 0..* DataType Reference(Device|Substance|Medication) for usecases in which the ChargeItem depends on a specific instance of the delivered product (e.g. with expensive and rare products, the price may vary per instance).

We can not always assume that there's an fully FHIR-documented associated workflow e.g. SupplyDelivery, MedicationDispenst that we can rely on to connect the ChargeItem with the product instance.

In many cases such documentation might be overkill.

A direct reference from ChargeItem would also allow in the simplest case to use a logical identifier to connect the ChargeItem with the instance identifier of the product without the need for Iimplementation additional Resources.