"As a part of a CDS Hooks response, if there is a need for further information then the payer IT system SHALL return a Card object with at least one Link object populated in the Card.links property. Otherwise no Link object would be provided. The Link object SHALL have a type property set to smart. The Link object SHALL have a URL property set to the launch URL of the DTR process."

I'd like to reconsider requiring that the launch URL must be sent by the payer in their CDS Hooks response. Using the presence of the link object as the indication that the DTR process must occur could become problematic if the DTR launch URL is not known by the payer.

It is reasonable to assume that payers know the URL of DTR applications hosted by the payer or a payer-chosen third party.

However, in the case that the DTR application is a native EHR app or a provider-chosen third party app, the payer will need to negotiate with each contracted provider to learn their specific launch URL, only to send it back to them in the response. 

This will require configuration in each payer's system and site-by-site negotiation with all involved parties. What automated alternatives might exist that will ease implementation and reduce the barrier to entry? If a payer does not have its own DTR app because every contracted provider has an app, should they send some canonical URL instead?

Further, if a payer sends a DTR launch URL, is the provider system obligated to use it if they have their own DTR application?