Payments

Gully Pay is the payment gateway for every Gully product, games included. In-game purchases, paid calls and top-ups go through Gully Pay checkout and webhooks, not through a store's own crypto code or a separate card processor wired into the game.

There are two shapes of payment:

#x402 pay-per-call

x402 uses the HTTP status 402 Payment Required. Your server answers a request with 402 and its payment requirements; the client pays on chain and retries with the payment in the X-PAYMENT header; your server verifies the payment with Gully Pay and serves the resource.

game ──GET /paid/level-7──────────────▶ your server
     ◀──402 + requirements──────────────
game ──pays on Gully Chain (ITransactionSender)
game ──GET /paid/level-7 + X-PAYMENT──▶ your server ──verify (API key)──▶ Gully Pay API
     ◀──200 + content───────────────────

In Unity, X402Client does the whole client side:

using GullyLabs.GameSdk;

var x402 = new X402Client();              // PreferredNetwork = "gully-chain-testnet"
var result = await x402.GetAsync("https://your-backend.example/paid/level-7", mySender);

Step by step, if you need control over each part:

X402Requirements req = X402Client.ParseRequirements(response);  // from the 402
X402Accept option    = x402.Choose(req);                        // picks the Gully Chain option
TransactionRequest tx = X402Client.BuildPaymentTx(option);      // send it from the player's account

#Verification happens on your server

The game never talks to the Gully Pay API with a key. Your resource server receives the X-PAYMENT header and verifies it by calling the Gully Pay API (https://gullypay.xyz/api, GullyChain.GullyPayApi) with its own Gully Pay API key. Only after Gully Pay confirms the payment does the server return the content.

#Checkout for in-game purchases

For item and currency purchases, the flow is the standard Gully Pay merchant flow:

1. Your game server creates a checkout for the player and the item.
2. The game opens the hosted checkout page (checkout.gullypay.xyz) in the system browser or a web view.
3. The player pays; Gully Pay settles on Gully Chain.
4. Gully Pay calls your server's webhook; the server verifies the signature and grants the item (in Nakama storage, on chain, or both).
5. The game refreshes the player's inventory from the server.

Grant items only from the verified webhook, never from a client-side "payment done" message.

#glUSD on the testnet

glUSD ("Gully USD") is Gully Pay's stablecoin. On Gully Chain Testnet it is minted 1:1 against USDC.e by a PSM (peg stability module) and is always redeemable 1:1 for USDC.e.

var bal = await Erc20.BalanceOfAsync(rpc, "0xDBE84bE6496Fb3d07F601548555ec7Acc4CeBa8F", player);

#Rules

• All billing goes through Gully Pay.
• Prices shown in the game come from the server, not from constants in the build.
• Every grant is idempotent: a webhook can arrive twice.
• Keep a server-side record of each purchase for refunds and support.