diff --git a/src/app/app.ts b/src/app/app.ts
index 81367c7..4162a3f 100644
--- a/src/app/app.ts
+++ b/src/app/app.ts
@@ -19,4 +19,4 @@ restate
   .bindKeyedRouter(userSessionApi.path, userSessionRouter)
   .bindKeyedRouter(ticketServiceApi.path, ticketDbRouter)
   .bindRouter(checkoutApi.path, checkoutRouter)
-  .listen(8080);
+  .listen(9080);
diff --git a/src/auxiliary/email_client.ts b/src/auxiliary/email_client.ts
index 1e41cbf..8125d8d 100644
--- a/src/auxiliary/email_client.ts
+++ b/src/auxiliary/email_client.ts
@@ -13,13 +13,13 @@ export class EmailClient {
   public static get() {
     return new EmailClient();
   }
-  public notifyUserOfPaymentSuccess(userId: string): boolean {
+  async notifyUserOfPaymentSuccess(userId: string): Promise<boolean> {
     console.log(`Notifying user ${userId} of payment success`);
     // send the email
     return true;
   }
 
-  public notifyUserOfPaymentFailure(userId: string): boolean {
+  async notifyUserOfPaymentFailure(userId: string): Promise<boolean> {
     console.log(`Notifying user ${userId} of payment failure`);
     // send the email
     return true;
diff --git a/src/part1/app.ts b/src/part1/app.ts
index 81367c7..4162a3f 100644
--- a/src/part1/app.ts
+++ b/src/part1/app.ts
@@ -19,4 +19,4 @@ restate
   .bindKeyedRouter(userSessionApi.path, userSessionRouter)
   .bindKeyedRouter(ticketServiceApi.path, ticketDbRouter)
   .bindRouter(checkoutApi.path, checkoutRouter)
-  .listen(8080);
+  .listen(9080);
diff --git a/src/part2/app.ts b/src/part2/app.ts
index 81367c7..4162a3f 100644
--- a/src/part2/app.ts
+++ b/src/part2/app.ts
@@ -19,4 +19,4 @@ restate
   .bindKeyedRouter(userSessionApi.path, userSessionRouter)
   .bindKeyedRouter(ticketServiceApi.path, ticketDbRouter)
   .bindRouter(checkoutApi.path, checkoutRouter)
-  .listen(8080);
+  .listen(9080);
diff --git a/src/part3/app.ts b/src/part3/app.ts
index 81367c7..4162a3f 100644
--- a/src/part3/app.ts
+++ b/src/part3/app.ts
@@ -19,4 +19,4 @@ restate
   .bindKeyedRouter(userSessionApi.path, userSessionRouter)
   .bindKeyedRouter(ticketServiceApi.path, ticketDbRouter)
   .bindRouter(checkoutApi.path, checkoutRouter)
-  .listen(8080);
+  .listen(9080);
diff --git a/src/part3/checkout.ts b/src/part3/checkout.ts
index ba8cd78..5fda161 100644
--- a/src/part3/checkout.ts
+++ b/src/part3/checkout.ts
@@ -26,20 +26,16 @@ const checkout = async (
 
   const paymentClient = PaymentClient.get();
 
-  const success = await paymentClient.call(idempotencyKey, totalPrice);
+  const success = await ctx.sideEffect(() => paymentClient.call(idempotencyKey, totalPrice));
 
   const email = EmailClient.get();
 
   if (success) {
     console.info("Payment successful. Notifying user about shipment.");
-    await ctx.sideEffect(async () =>
-      email.notifyUserOfPaymentSuccess(request.userId),
-    );
+    await ctx.sideEffect(() => email.notifyUserOfPaymentSuccess(request.userId));
   } else {
     console.info("Payment failure. Notifying user about it.");
-    await ctx.sideEffect(async () =>
-      email.notifyUserOfPaymentFailure(request.userId),
-    );
+    await ctx.sideEffect( () => email.notifyUserOfPaymentFailure(request.userId));
   }
 
   return success;
diff --git a/src/part4/app.ts b/src/part4/app.ts
index 81367c7..4162a3f 100644
--- a/src/part4/app.ts
+++ b/src/part4/app.ts
@@ -19,4 +19,4 @@ restate
   .bindKeyedRouter(userSessionApi.path, userSessionRouter)
   .bindKeyedRouter(ticketServiceApi.path, ticketDbRouter)
   .bindRouter(checkoutApi.path, checkoutRouter)
-  .listen(8080);
+  .listen(9080);
diff --git a/src/part4/checkout.ts b/src/part4/checkout.ts
index 52b80cc..6b837ce 100644
--- a/src/part4/checkout.ts
+++ b/src/part4/checkout.ts
@@ -26,22 +26,17 @@ const checkout = async (
 
   const paymentClient = PaymentClient.get();
 
-  const doPayment = async () =>
-    paymentClient.failingCall(idempotencyKey, totalPrice);
+  const doPayment = () => paymentClient.failingCall(idempotencyKey, totalPrice);
   const success = await ctx.sideEffect(doPayment);
 
   const email = EmailClient.get();
 
   if (success) {
     console.info("Payment successful. Notifying user about shipment.");
-    await ctx.sideEffect(async () =>
-      email.notifyUserOfPaymentSuccess(request.userId),
-    );
+    await ctx.sideEffect( () => email.notifyUserOfPaymentSuccess(request.userId));
   } else {
     console.info("Payment failure. Notifying user about it.");
-    await ctx.sideEffect(async () =>
-      email.notifyUserOfPaymentFailure(request.userId),
-    );
+    await ctx.sideEffect(() => email.notifyUserOfPaymentFailure(request.userId));
   }
 
   return success;