Thanks saeidw :)
Ok now another question... How does the following translate into an HTTP request:
curl -k -u MERCHANT_ID:MERCHANT_KEY -d "_type=hello" "https://sandbox.google.com/checkout/api/checkout/v2/requestForm/Merchant/MERCHANT_ID"
What I am trying to say, if I have an HTML form, what would be the action attribute? Only the url part or does _type get appended some way?