How can I correctly use ClassTag with unmarshal?

It seems like I don't fully understand how TypeTags and ClassTags work. I'm trying to create generic function that makes http REST call using Spray. It looks like this

def sendRequest[RQ, RS](userId: String, endPoint: String, body: RQ): Future[RS] = {

  val pipeline =
    sendReceive ~>
    decode(Gzip) ~>
    decode(Deflate) ~>
    unmarshal[RS]

  pipeline(Post("http://something", body))
}

which I attempt to use like this

val result: Future[FetchStreamsResponse] = sendRequest(userId, "v1/get_streams", body)

It gave Error:(161, 18) could not find implicit value for evidence parameter of type spray.httpx.unmarshalling.FromResponseUnmarshaller[RS] unmarshal[RS] of course. I tried specifying type as RS : ClassTag : TypeTag but it didn't help. Does use of class tag requires modification of unmarshal function too ? What shall I do ?