diff --git a/main.ts b/main.ts
index 1b7df5d..6675523 100644
--- a/main.ts
+++ b/main.ts
@@ -2,7 +2,13 @@ import { serve } from "wren/mod.ts";
 import { GET, POST } from "wren/route.ts";
 import * as Response from "wren/response.ts";
 import { AppManifest } from "./types.ts";
-import { cancelSub, chargeSub, refundSub } from "./subscriptions.ts";
+import {
+  cancelSub,
+  chargeSub,
+  gatewayInitialize,
+  refundSub,
+  transactionInitialize,
+} from "./subscriptions.ts";
 
 interface ActionRequestResponse {
   pspReference: string;
@@ -50,6 +56,18 @@ const routes = [
       permissions: ["HANDLE_PAYMENTS", "HANDLE_CHECKOUTS", "MANAGE_ORDERS"],
       tokenTargetUrl: `${URL}/install`,
       webhooks: [
+        {
+          name: "Gateway Initialize",
+          targetUrl: `${URL}/gateway-initialize`,
+          query: gatewayInitialize,
+          syncEvents: ["PAYMENT_GATEWAY_INITIALIZE_SESSION"],
+        },
+        {
+          name: "Transaction Initialize",
+          targetUrl: `${URL}/transaction-initialize`,
+          query: transactionInitialize,
+          syncEvents: ["TRANSACTION_INITIALIZE_SESSION"],
+        },
         {
           name: "Charge Request",
           targetUrl: `${URL}/transaction-charge-requested`,
@@ -85,6 +103,27 @@ const routes = [
       success: true,
     });
   }),
+  POST("/gateway-initialize", async (req: Request) => {
+    const json = await req.json();
+    console.log("gateway initialize", json);
+    console.log("headers", req.headers);
+    return Response.OK({
+      data: {
+        some: "data",
+      },
+    });
+  }),
+  POST("/transaction-initialize", async (req: Request) => {
+    const json = await req.json();
+    console.log("transaction initialize", json);
+    console.log("headers", req.headers);
+    const amount = json.action.amount;
+    return Response.OK({
+      pspReference: "initialize-test",
+      result: "CHARGE_SUCCESS",
+      amount,
+    });
+  }),
   POST("/transaction-charge-requested", async (req: Request) => {
     const json = await req.json();
     console.log("charge request", json);
diff --git a/subscriptions.ts b/subscriptions.ts
index 0ea0597..f5032c6 100644
--- a/subscriptions.ts
+++ b/subscriptions.ts
@@ -1,3 +1,58 @@
+export const gatewayInitialize = `subscription {
+  event {
+    ... on PaymentGatewayInitializeSession {
+      issuedAt
+      version
+      issuingPrincipal {
+        ... on Node {
+          id
+        }
+        __typename
+      }
+      recipient {
+        id
+        name
+      }
+      sourceObject {
+        __typename
+      }
+      data
+      amount
+    }
+  }
+}`;
+
+export const transactionInitialize = `subscription {
+  event {
+    ... on TransactionInitializeSession {
+      issuedAt
+      version
+      issuingPrincipal {
+        ... on Node {
+          id
+        }
+        __typename
+      }
+      recipient {
+        id
+        name
+      }
+      transaction {
+        id
+        name
+        pspReference
+      }
+      data
+      merchantReference
+      action {
+        amount
+        currency
+        actionType
+      }
+    }
+  }
+}`
+
 export const chargeSub = `subscription {
   event {
     ... on TransactionChargeRequested {
@@ -20,7 +75,7 @@ export const chargeSub = `subscription {
     }
   }
 }
-`
+`;
 
 export const refundSub = `subscription {
   event {
@@ -43,7 +98,7 @@ export const refundSub = `subscription {
       }
     }
   }
-}`
+}`;
 
 export const cancelSub = `subscription {
   event {
@@ -66,4 +121,4 @@ export const cancelSub = `subscription {
       }
     }
   }
-}`
+}`;