you need to Set up and select Environment for Checkout, which contains information on host, keys and hash. Environment settings can be updated manually or by importing JSON-format file. JSON file and/or values (CHECKOUT_HOST, merch1_pass_post, variable_key) are provided by Account manager or created manually in the Merchants section of your dashboard . checkout this pdf:https://montypay.com/Postman-Request-Sending.pdf