> ## Documentation Index > Fetch the complete documentation index at: https://docs.appcharge.com/llms.txt > Use this file to discover all available pages before exploring further. # About the Server-to-Server Model In this flow, a server-to-server communication occurs. After a purchase, Appcharge triggers a webhook to the publisher’s backend with the transaction details. The publisher's server updates the player's balance accordingly. **High-Level Flow:** 1. **Player clicks to purchase** The player selects an item to purchase from the in-game store. The game server initiates server-to-server communication with Appcharge's backend to handle the checkout process. 2. **Create Checkout Session** The game server uses the SDK to request from Appcharge’s backend a session that contains all the details needed for opening the checkout. This session setup involves localization, tax calculations, and payment method preparation, all managed through server-to-server API calls. 3. **Checkout Response** The SDK receives a response from the backend confirming that a checkout session has been successfully created. This response includes all the necessary information to proceed with the payment. 4. **Acknowledgement** Once the payment is successfully processed, Appcharge's backend sends a confirmation directly to the game server. This confirmation acknowledges that the purchase was successful and that the player will receive the purchased item. 5. **Balance Update** Following the confirmation, the game server updates the player’s balance in the game to reflect the purchase, thereby completing the transaction.