#23649 merged RSocketRequester.RequestSpec and RSocketRequester.ResponseSpec into one and as a consequence the below is now possible which would send the 3rd data value "Hello 3" as the payload data and ignore the first two:

Flux<String> result = requester.route("route")
    .data("Hello 1")
    .data("Hello 2")
    .data("Hello 3")
    .retrieveFlux(String.class);

This was not an intended consequence that should not have been introduced. This issue is to correct it and ensure that after the first call to data, it is only possible to see the options for retrieving the response.