Description: Sent when client opens Downloader
Request: ID, CountriesV, PurchasesV
{
  "ID":"12345",                   // unique client id
  "Cmd":"VersionCheck",
  "Params":
  {
    "CountriesV":1,               // local version of countries file on the client
    "PurchasesV":1,               // local version of purchases file on the client
    "ClientV":1                   // client version
  }
}
Response: Credit [, CountriesV, Countries, PurchasesV, Purchases]
{
  "Credit":10,                    // current credit for the client
  "CountriesV":2,                 // optional, latest version of countries list
  "Countries":{...},              // optional, latest countries list with new prices and new countries
  "PurchasesV":2,                 // optional, latest inapp purchases list version
  "Purchases":["123","456","789"]  // optional, latest inapp purchases IDS
}

Description: Sent by client to validate payment and add credits
Request: ID, Receipt
{
  "ID":"12345",
  "Cmd":"ValidatePayment",
  "Params":
  {
    "Receipt":"ASD24@#$!@$%"        // base 64 encoded app store receipt to validate and store on our server
  }
}
Response: Credit [, Error]
{
  "Credit":23,                          // current credit for the client
  "Error":"Invalid purchase receipt"    // optional, sent if receipt was not validated by Apple server
}

Description: Sent by client to add some credit by entering friend promo code or any other public promo code
Request: ID, Code
{
  "ID":"12345",
  "Cmd":"ValidatePromoCode",
  "Params":
  {
    "Code":"123asdREWR24ad"
  }
}
Response: Credit [, Error]
{
  "Credit":27,                            // current credit for the client
  "Error":"Promo Code is already used"    // optional, sent if promo code is invalid
}

Description: Sent by client when he tries to download the country file
Request: ID, Version, File, Size
{
  "ID":"12345",
  "Cmd":"Download",
  "Params":
  {
    "Version":110920,
    "File":"Belarus.mwm",
    "Size":47123456
  }
}
Response: File[, Urls | Error]
{
  "File":"Belarus.mwm",
  "Urls":["http://blablalba.com/casd/234dsf","http://asd.com/fda/qwert"],  // special urls valid only for this client to download given file
  "Error":"Invalid file or no credit"     // sent if no credit is left instead of Urls
}

Description: Client requests own "Bring friend" code once, which should be entered as Promo code by any friend
Request: ID, FriendCode
{
  "ID":"12345",
  "Cmd":"FriendCode",
}
Response: FriendCode
{
  "FriendCode":"ASDF123Gsdf342"  // unique promo code for this client, to bring his friends
}