diff --git a/src/domain/Challenge.ts b/src/domain/Challenge.ts
index 155a410..2fbd82c 100644
--- a/src/domain/Challenge.ts
+++ b/src/domain/Challenge.ts
@@ -43,6 +43,7 @@ import { V5_TRACK_IDS_TO_NAMES, V5_TYPE_IDS_TO_NAMES } from "../common/Conversio
 import PaymentCreator, { PaymentDetail } from "../util/PaymentCreator";
 import { getChallengeResources } from "../api/v5Api";
 import m2mToken from "../helpers/MachineToMachineToken";
+import { sendHarmonyEvent } from "../helpers/Harmony";
 
 if (!process.env.GRPC_ACL_SERVER_HOST || !process.env.GRPC_ACL_SERVER_PORT) {
   throw new Error("Missing required configurations GRPC_ACL_SERVER_HOST and GRPC_ACL_SERVER_PORT");
@@ -267,6 +268,7 @@ class ChallengeDomain extends CoreOperations<Challenge, CreateChallengeInput> {
       };
 
       newChallenge = await super.create(challenge, metadata);
+      await sendHarmonyEvent("CREATE", "Challenge", newChallenge, input.billing?.billingAccountId!);
     } catch (err) {
       // Rollback lock amount
       if (baValidation != null) {
@@ -536,6 +538,19 @@ class ChallengeDomain extends CoreOperations<Challenge, CreateChallengeInput> {
       };
 
       updatedChallenge = await super.update(scanCriteria, dataToUpdate, metadata);
+
+      const newChallenge = updatedChallenge.items[0];
+      if (newChallenge.billing?.billingAccountId !== challenge?.billing?.billingAccountId) {
+        // For a New/Draft challenge, it might miss billing account id
+        // However when challenge activates, the billing account id will be provided (challenge-api validates it)
+        // In such case, send a CREATE event with whole challenge data (it's fine for search-indexer since it upserts for CREATE)
+        // Otherwise, the outer customer specified by the billing account id (like Topgear) will never receive a challenge CREATE event
+        await sendHarmonyEvent("CREATE", "Challenge", newChallenge, newChallenge.billing?.billingAccountId);
+      } else {
+        // Send only the updated data
+        // Some field like chanllege description could be big, don't include them if they're not actually updated
+        await sendHarmonyEvent("UPDATE", "Challenge", { ...dataToUpdate, id: newChallenge.id }, newChallenge.billing?.billingAccountId);
+      }
     } catch (err) {
       if (baValidation != null) {
         await lockConsumeAmount(baValidation, true);
@@ -725,12 +740,14 @@ class ChallengeDomain extends CoreOperations<Challenge, CreateChallengeInput> {
       if (baValidation != null) await lockConsumeAmount(baValidation);
       try {
         await super.update(scanCriteria, dynamoUpdate);
+        await sendHarmonyEvent("UPDATE", "Challenge", { ...data, id }, challenge.billing?.billingAccountId);
       } catch (err) {
         if (baValidation != null) await lockConsumeAmount(baValidation, true);
         throw err;
       }
     } else {
       await super.update(scanCriteria, dynamoUpdate);
+      await sendHarmonyEvent("UPDATE", "Challenge", { ...data, id }, challenge.billing?.billingAccountId);
       console.log("Challenge Completed");
 
       const completedChallenge = await this.lookup(DomainHelper.getLookupCriteria("id", id));
@@ -805,6 +822,7 @@ class ChallengeDomain extends CoreOperations<Challenge, CreateChallengeInput> {
 
     try {
       const result = await super.delete(lookupCriteria);
+      await sendHarmonyEvent("DELETE", "Challenge", { id: challenge.id }, challenge.billing?.billingAccountId);
       return result;
     } catch (err) {
       await lockConsumeAmount(baValidation, true);
diff --git a/src/helpers/Harmony.ts b/src/helpers/Harmony.ts
new file mode 100644
index 0000000..ebf9a2c
--- /dev/null
+++ b/src/helpers/Harmony.ts
@@ -0,0 +1,46 @@
+import _ from "lodash";
+import { InvokeCommand, LambdaClient } from "@aws-sdk/client-lambda";
+
+import { EVENT_ORIGINATOR } from "../common/Constants";
+
+const FunctionName =
+  process.env.HARMONY_LAMBDA_FUNCTION ??
+  "arn:aws:lambda:us-east-1:811668436784:function:harmony-api-dev-processMessage";
+
+const harmonyClient = new LambdaClient({ region: process.env.AWS_REGION, maxAttempts: 2 });
+
+/**
+ * Send event to Harmony.
+ * @param eventType The event type
+ * @param payloadType The payload type
+ * @param payload The event payload
+ * @param billingAccountId The billing account id
+ */
+export async function sendHarmonyEvent(eventType: string, payloadType: string, payload: object, billingAccountId?: number) {
+  const event = {
+    publisher: EVENT_ORIGINATOR,
+    timestamp: new Date().getTime(),
+    eventType,
+    payloadType,
+    payload,
+    billingAccountId,
+  };
+
+  const invokeCommand = new InvokeCommand({
+    FunctionName,
+    InvocationType: "RequestResponse",
+    Payload: JSON.stringify(event),
+    LogType: "None"
+  });
+
+  const result = await harmonyClient.send(invokeCommand);
+
+  if (result.FunctionError) {
+    console.error(
+      "Failed to send Harmony event",
+      result.FunctionError,
+      result.Payload?.transformToString()
+    );
+    throw new Error(result.FunctionError);
+  }
+}