Timeouts in reverse proxy

I am trying to set timeouts for a proxy target that will lead to a termination in case of a very slow upload. I am using the options read_timeout, but nothing seems to be happening. The same applies to write_timeout.

handle_path /upload_target/* {
    reverse_proxy http://upload_target:8081 {
        transport http {
            read_timeout 10s
            write_timeout 10s            
         }
    }
}

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