Viewers make purchases through the Twitch Extension Bits Monetization API.
Use the Twitch Developer Rig to create a set of purchasable products.

Sending Purchases from Twitch to GameLink

After a product is purchased, the Twitch extension helper invokes the callback
passed into twitch.ext.bits.onTransactionComplete().

In this callback, the client extension should do the following:

• Check to see if the initiator is current_user, in order to prevent extra calls to the GameLink server.
• POST any purchases initiated by current_user to the bits/transactions endpoint.

For example this.sdk.signedRequest("POST", "bits/transactions", JSON.stringify(transaction));

The following example implements a full onTransactionComplete callback method.

var sdk = new Muxy.SDK();
// ... 
twitch.ext.bits.onTransactionComplete((tx) => {
  if (tx.initiator === "CURRENT_USER" || tx.initiator === "current_user") {
    sdk.signedRequest("POST", "bits/transactions", JSON.stringify(tx));
  }
});

GameLink validates and deduplicates these transactions to prevent replays.

Receiving Purchase Events

A client can subscribe to Bits Purchase notifications through a WebSocket connection. You can listen for transactions involving a specific product, or for all products you offer. Products are identified by SKU.

Subscribe to purchase events

Send a message using the subscribe action with a transaction_complete target.
The data sku field contains the SKU value for the product being purchased, or the special character * to listen for all product transactions.

{
  "action": "subscribe",
  "params": {
    "request_id": 200,
    "target": "transaction_complete"
  },
    "data": {
    "sku": "my_sku"
  }
}

❗️

Product-specific filter not yet available

Currently, clients receive all transaction_complete messages regardless of subscription status

Transaction event notifications

Whenever a user makes a valid bits purchase, the following message is sent to all listening
clients.

{
    "action": "update", 
    "params": {
        "request_id": 0xffff, 
        "target": "transaction_complete", 
    },

    "data": {
        "sku": "some-sku", 
        "displayName": "Product Display Name", 
        "cost": <bits cost>, 
        "userId": "<twitch user_id of purchaser>", 
        "timestamp": <unix timestamp of purchase>, 
        "id": "<transaction id>", 
        "username": "<twitch display username of purchaser>"
    }
}

Note that the username value is completely user-controlled.