Reference:  https://chat.fhir.org/#narrow/stream/197730-Da-Vinci.20PDex.20Drug.20Formulary/topic/CostSharing.20.20Extension

The available selections for CopayOption and CoinsuranceOption don't seem to fit if the Medicaid Plan has a deductible of $0. All of these would mislead the member if there is no deductible:
after-deductible
before-deductible
no-charge
no-charge-after-deductible

Is there something we're missing? We can use "after-deductible" for now but recommend adding another selection that is specific to this situation for the next build.

The structure/definition of the cost sharing extensions were (rightly or wrongly) based on the QHP Formulary – see https://github.com/CMSgov/QHP-provider-formulary-APIs#cost-sharing-sub-type.

The QHP Formulary definition is a bit thin on how to actually use the fields.
Looking at the 2021 instructions for registering a QHP formulary (see https://www.hhs.gov/guidance/sites/default/files/hhs-guidance-documents/QHP_Slides_040220_5CR_040220_8.pdf, starting at slide 21) there is a bit more detail.

1) There is an additional value of "Not Applicable" for both the CopayOption and the CoInsuranceOption.
2) There is a plan-level text field for any explanation of features that don't fit well into the structure.
3) Zero-Cost Drugs, two options are presented:
 - CoPaymentOption: N/A, CoInsuranceOption: No Charge, or

• CoPaymentOptiion: No Charge, CoInsuranceOption: N/A
  4) Business rule says you can't specify N/A for both CoPaymentOption and CoInsuranceOption

Seems like we are missing the N/A values for both CopaymentOption and CoinsuranceOption, and some guidance on how to handle some of the expected corner cases.