Data transfer between Merchant and myPOS Checkout is made by HTTP POST. All the parameters for the requests are in the body in [parameter=value] form. Separator between tokens is [&]. The body is URL Encoded. Character encoding is UTF-8.
Example: POST /somescript.php HTTP/1.1 Host: www.somesite.com User-Agent: Mozilla/4.0 Content-Length: 39 Content-Type: application/x-www-form-urlencoded userid=joe&password=guessme&user_type=1