If your integration platform is calling our FHIR services, it is essentially an "app" - though I would assume this means the app will be using B2B access or access on behalf of a system (which isn't available in prod yet). You are required to be part of our developer program in order to resell that application to our clients, and would need to do development against our sandbox here prior to applying to the program (otherwise it would be very difficult to answer some of the questions around gaps and app id required for that application).
If you have a client you are partnering with, that is also listed on the application to become part of the code program.
Once you are in the program, we supply the FHIR URL as part of the process when you test with a client, as well as whitelisting your application for those clients/tenants with their approval.
If you are referring to something other than our ignite platform/Cerner's implementation of FHIR, this forum isn't going to have that answer :) You would need to reach out to clients to see what options they have to integrate with their systems (eg: V2 interfaces).