I asked a very similar question here
The thing that came out of it that I think you should think about is that there's no need to add Get / Post etc. to the interface. You can handle all that with extension methods. The answer to my question helped me with that. Here's the interface that I ended up with. Much simpler.
For your first Go program this looks very good, apart from the global
variables the code looks easy to read; the annotations for JSON
processing and validation are fine and you're also using a standard
library for the routing. Overall, doesn't raise any big issues for me.
Firstly though, I'd highly suggest that the trades and submitArray
global variables ...