The COBOL program has to call the new HTTP service

The new claims service is HTTP. The nightly COBOL job still has to call it. How does the host program reach it?

Generate a COBOL or RPG client so the legacy program calls the modern HTTP API. That is a Reverse API: the host calls out, it is not an inbound asset you add on the host. Generate the client from a Hub REVERSE method or from an OpenAPI file, set the code page, compile, and call through OLREVAPI. Keep the new service's contract as the source of the client.