Problem with InOnly exchange pattern using with RestDSL

Hello! I'm using spark-java as rest-dsl provider (but I already tried with
the servlet component and still didn't work) and I'm having some issues
using in only in a rest dsl route:

That's the rest configuration:
restConfiguration().component("spark-rest").bindingMode(RestBindingMode.json)
.dataFormatProperty("prettyPrint", "true");

my endpoint:

rest("/rs/tm").consumes(APPLICATION_RESOURCE_JSON).produces(APPLICATION_RESOURCE_JSON)
.post().outType(Transaction.class).type(Transaction.class)
.to("direct:processTransaction");

and, my direct:processTransaction:

from("direct:processTransaction")
.process(e -> {
//doing really funny stuff over here
})
.inOnly("seda:processTransaction");

so... whenever i try to send a message to an endpoint using InOnly exchange
pattern, the rest-dsl endpoint gets messed up, for example, it is not
converted automatically to json before returning to the client, and also
content type is not set, but, when I try to use the InOut pattern,
everything works fine, but I really need this endpoint to be async at that
point.
oh, and yeah, when I don't set the InOnly pattern before calling the seda
endpoint, the message is sent sync, i have no idea why.

does anyone know what could be happening?

waiting for an answer, thanks!!