How do I send a JSON string in a POST request in Go

I tried working with Apiary and made a universal template to send JSON to mock server and have this code: package main import ( "encoding/json" "fmt" "github.com/jmcvetta/napping" "log" "net/http" ) func main() { url := "http://restapi3.apiary.io/notes" fmt.Println("URL:>", url) s := napping.Session{} h := &http.Header{} h.Set("X-Custom-Header", "myvalue") s.Header = h var jsonStr = []byte(`{ "tit