Accessing POST payload from cxfrs invocation

I have a configured cxf rsServer, which kicks off a camel route that then
passes the request along to another service configured as a cxf rsClient
endpoint. Both are POST operations. This mostly works well, except for the
POST payload being sent to the second service.

The first service contains two URL parameteres, so the definition looks
something like this:

@POST
@Path("/foo/{param1}/bar/{param2}/op")
@Consumes(MediaType.APPLICATION_JSON")
public Response fooBar(@PathParam("param1")String param1,
@PathParam("param2")String param2, Map<String, String> payload);

The problem is that although when the initial request comes in the
LoggingInterceptor prints my payload as:

Address: http://localhost:8182/foo/valueOfParam1/bar/valueOfParam2/op
...
Payload: { "one" : "number1", "two" : "number2" }

it then sets the payload for the second to the value of param1:

Address:
http://localhost:8080/restpath/foo/valueOfParam1/bar/valueOfParam2/op
...
Payload: valueOfParam1

I would have assumed that it would forward the initial request's POST
payload as the payload for the second service but, since it doesn't, how
can I set the payload so that I get this result? I thought it would be easy
to find this documented, but unfortunately haven't been able to (apologies
if I'm missing something obvious).

TIA