Debugging bad requests with vibe

[Nicholas Wilson]

I have set up a vibe.d rest interface (on a server) and have a 
client on my machine.

struct Observation
{
     string desc;
     DateTime time;
}

interface Obsever
{
     @property void observe(Observation ra);
}

void main()
{
     auto test = Observation("a duck", 
cast(DateTime)Clock.currTime(UTC()));

     auto client = new RestInterfaceClient! 
Obsever("http://example.com/observation");
     client. observe = test; // 400
}

I' pretty sure the url is correct because other ones give 404.

Is there a way I can see/log what requests are being made? I can 
change both the client and server.