This is the advanced path, so use make_game unless the sender asks you to write the game yourself. It saves a complete self-contained HTML game you wrote as a free private draft, and returns a preview link (previewUrl) and a private managementToken. Build the gameplay around the sender's details, with inline CSS and JavaScript, embedded assets, keyboard and touch controls, a goal and a restart. The game can't make network requests or take payments. Generate a random 32-byte hex idempotencyKey and reuse it only to retry the same request. Keep the managementToken private.