diff --git a/src/emitters.ts b/src/emitters.ts
index 83d746ef..c1777010 100644
--- a/src/emitters.ts
+++ b/src/emitters.ts
@@ -90,11 +90,13 @@ export type OnMessageArgs = {
      *
      * @param response - The message to send as a reply
      * @param context - Wether to mention the current message, defaults to false
+     * @param biz_opaque_callback_data - An arbitrary 256B string, useful for tracking
      * @returns WhatsAppAPI.sendMessage return value
      */
     reply: (
         response: ClientMessage,
-        context?: boolean
+        context?: boolean,
+        biz_opaque_callback_data?: string
     ) => Promise<ServerMessageResponse | Response>;
     /**
      * The WhatsAppAPI instance that emitted the event
@@ -142,6 +144,10 @@ export type OnStatusArgs = {
      * The error object
      */
     error?: ServerError;
+    /**
+     * Arbitrary string included in sent messages
+     */
+    biz_opaque_callback_data?: string;
     /**
      * The raw data from the API
      */
diff --git a/src/index.ts b/src/index.ts
index daa49b5c..401ab8b1 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -204,13 +204,15 @@ export default class WhatsAppAPI {
      * @param to - The user's phone number
      * @param message - A Whatsapp message, built using the corresponding module for each type of message.
      * @param context - The message ID of the message to reply to
+     * @param biz_opaque_callback_data - An arbitrary 256B string, useful for tracking (length not checked by the framework)
      * @returns The server response
      */
     async sendMessage(
         phoneID: string,
         to: string,
         message: ClientMessage,
-        context?: string
+        context?: string,
+        biz_opaque_callback_data?: string
     ): Promise<ServerMessageResponse | Response> {
         const type = message._type;
 
@@ -228,6 +230,8 @@ export default class WhatsAppAPI {
             message._build();
 
         if (context) request.context = { message_id: context };
+        if (biz_opaque_callback_data)
+            request.biz_opaque_callback_data = biz_opaque_callback_data;
 
         // Make the post request
         const promise = this.fetch(
@@ -784,12 +788,13 @@ export default class WhatsAppAPI {
                 message,
                 name,
                 raw: data,
-                reply: (response, context = false) =>
+                reply: (response, context = false, biz_opaque_callback_data) =>
                     this.sendMessage(
                         phoneID,
                         from,
                         response,
-                        context ? message.id : undefined
+                        context ? message.id : undefined,
+                        biz_opaque_callback_data
                     ),
                 Whatsapp: this
             };
@@ -804,6 +809,7 @@ export default class WhatsAppAPI {
             const conversation = statuses.conversation;
             const pricing = statuses.pricing;
             const error = statuses.errors?.[0];
+            const biz_opaque_callback_data = statuses.biz_opaque_callback_data;
 
             const args: OnStatusArgs = {
                 phoneID,
@@ -813,6 +819,7 @@ export default class WhatsAppAPI {
                 conversation,
                 pricing,
                 error,
+                biz_opaque_callback_data,
                 raw: data
             };
 
diff --git a/src/types.ts b/src/types.ts
index 4c95baa1..a99289fd 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -326,9 +326,9 @@ export type ClientMessageRequest = {
      */
     to: string;
     /**
-     * Undocumented, optional (the framework doesn't use it)
+     * Currently you can only send messages to individuals
      */
-    recipient_type?: "individual";
+    recipient_type: "individual";
     /**
      * The message to reply to
      */
@@ -338,6 +338,15 @@ export type ClientMessageRequest = {
          */
         message_id: string;
     };
+    /**
+     * An arbitrary 256B string, useful for tracking.
+     *
+     * Any app subscribed to the messages webhook field on the WhatsApp Business Account can get this string,
+     * as it is included in statuses object within webhook payloads.
+     *
+     * Cloud API does not process this field, it just returns it as part of sent/delivered/read message webhooks.
+     */
+    biz_opaque_callback_data?: string;
 } & (
     | {
           type: "text";
@@ -710,6 +719,7 @@ export type PostData = {
                               status: ServerStatus;
                               timestamp: string;
                               recipient_id: string;
+                              biz_opaque_callback_data?: string;
                           } & (
                               | {
                                     conversation: ServerConversation;
diff --git a/test/index.test.cjs b/test/index.test.cjs
index 28e41c10..47022530 100644
--- a/test/index.test.cjs
+++ b/test/index.test.cjs
@@ -388,6 +388,7 @@ describe("WhatsAppAPI", function () {
         const user = "3";
         const id = "something_random";
         const context = "another_random_id";
+        const tracker = "tracker";
 
         const type = "text";
         const message = new Text("Hello world");
@@ -406,6 +407,11 @@ describe("WhatsAppAPI", function () {
             }
         };
 
+        const requestWithTracker = {
+            ...request,
+            biz_opaque_callback_data: tracker
+        };
+
         const expectedResponse = {
             messaging_product: "whatsapp",
             contacts: [
@@ -478,6 +484,31 @@ describe("WhatsAppAPI", function () {
                 deepEqual(response, expectedResponse);
             });
 
+            it("should be able to send with a tracker (biz_opaque_callback_data)", async function () {
+                clientFacebook
+                    .intercept({
+                        path: `/${Whatsapp.v}/${bot}/messages`,
+                        method: "POST",
+                        headers: {
+                            Authorization: `Bearer ${token}`,
+                            "Content-Type": "application/json"
+                        },
+                        body: JSON.stringify(requestWithTracker)
+                    })
+                    .reply(200, expectedResponse)
+                    .times(1);
+
+                const response = await Whatsapp.sendMessage(
+                    bot,
+                    user,
+                    message,
+                    undefined,
+                    tracker
+                );
+
+                deepEqual(response, expectedResponse);
+            });
+
             it("should return the raw fetch response if parsed is false", async function () {
                 Whatsapp.parsed = false;
 
@@ -1419,6 +1450,10 @@ describe("WhatsAppAPI", function () {
     });
 
     describe("Webhooks", function () {
+        function threw(i) {
+            return (e) => e === i;
+        }
+
         describe("Get", function () {
             const mode = "subscribe";
             const challenge = "challenge";
@@ -1449,40 +1484,34 @@ describe("WhatsAppAPI", function () {
             });
 
             it("should throw 500 if webhookVerifyToken is not specified", function () {
-                const compare = (e) => e === 500;
-
                 delete Whatsapp.webhookVerifyToken;
 
                 throws(function () {
                     Whatsapp.get(params);
-                }, compare);
+                }, threw(500));
             });
 
             it("should throw 400 if the request is missing data", function () {
-                const compare = (e) => e === 400;
-
                 throws(function () {
                     Whatsapp.get({});
-                }, compare);
+                }, threw(400));
 
                 throws(function () {
                     Whatsapp.get({ "hub.mode": mode });
-                }, compare);
+                }, threw(400));
 
                 throws(function () {
                     Whatsapp.get({ "hub.verify_token": token });
-                }, compare);
+                }, threw(400));
             });
 
             it("should throw 403 if the verification tokens don't match", function () {
-                const compare = (e) => e === 403;
-
                 throws(function () {
                     Whatsapp.get(
                         { ...params, "hub.verify_token": "wrong" },
                         token
                     );
-                }, compare);
+                }, threw(403));
             });
         });
 
@@ -1520,6 +1549,7 @@ describe("WhatsAppAPI", function () {
                 billable: true,
                 category: "business-initiated"
             };
+            const biz_opaque_callback_data = "5";
 
             const valid_message_mock = new MessageWebhookMock(
                 phoneID,
@@ -1533,7 +1563,8 @@ describe("WhatsAppAPI", function () {
                 status,
                 id,
                 conversation,
-                pricing
+                pricing,
+                biz_opaque_callback_data
             );
 
             const Whatsapp = new WhatsAppAPI({
@@ -1553,47 +1584,39 @@ describe("WhatsAppAPI", function () {
             describe("Validation", function () {
                 describe("Secure truthy (default)", function () {
                     it("should throw 400 if rawBody is missing", function () {
-                        const compare = (e) => e === 400;
-
-                        rejects(Whatsapp.post(valid_message_mock), compare);
+                        rejects(Whatsapp.post(valid_message_mock), threw(400));
 
                         rejects(
                             Whatsapp.post(valid_message_mock, undefined),
-                            compare
+                            threw(400)
                         );
                     });
 
                     it("should throw 401 if signature is missing", function () {
-                        const compare = (e) => e === 401;
-
                         rejects(
                             Whatsapp.post(valid_message_mock, body),
-                            compare
+                            threw(401)
                         );
 
                         rejects(
                             Whatsapp.post(valid_message_mock, body, undefined),
-                            compare
+                            threw(401)
                         );
                     });
 
                     it("should throw 500 if appSecret is not specified", function () {
-                        const compare = (e) => e === 500;
-
                         delete Whatsapp.appSecret;
 
                         rejects(
                             Whatsapp.post(valid_message_mock, body, signature),
-                            compare
+                            threw(500)
                         );
                     });
 
                     it("should throw 401 if the signature doesn't match the hash", function () {
-                        const compare = (e) => e === 401;
-
                         rejects(
                             Whatsapp.post(valid_message_mock, body, "wrong"),
-                            compare
+                            threw(401)
                         );
                     });
 
@@ -1626,11 +1649,9 @@ describe("WhatsAppAPI", function () {
                 });
 
                 it("should throw 400 if the request isn't a valid WhatsApp Cloud API request (data.object)", function () {
-                    const compare = (e) => e === 400;
-
                     Whatsapp.secure = false;
 
-                    rejects(Whatsapp.post({}), compare);
+                    rejects(Whatsapp.post({}), threw(400));
                 });
             });
 
@@ -1776,6 +1797,7 @@ describe("WhatsAppAPI", function () {
                         id,
                         conversation,
                         pricing,
+                        biz_opaque_callback_data,
                         raw: valid_status_mock
                     });
                 });
diff --git a/test/webhooks.mocks.cjs b/test/webhooks.mocks.cjs
index fe6d9ca2..42e5974d 100644
--- a/test/webhooks.mocks.cjs
+++ b/test/webhooks.mocks.cjs
@@ -50,7 +50,15 @@ class StatusWebhookMock {
     /**
      * Helper class to test the status post request, conditionally creating the object based on the available data
      */
-    constructor(phoneID, phone, status, messageID, conversation, pricing) {
+    constructor(
+        phoneID,
+        phone,
+        status,
+        messageID,
+        conversation,
+        pricing,
+        biz_opaque_callback_data
+    ) {
         this.object = "whatsapp_business_account";
         this.entry = [
             {
@@ -95,6 +103,11 @@ class StatusWebhookMock {
             this.entry[0].changes[0].value.statuses[0].pricing = pricing;
         }
 
+        if (biz_opaque_callback_data) {
+            this.entry[0].changes[0].value.statuses[0].biz_opaque_callback_data =
+                biz_opaque_callback_data;
+        }
+
         if (
             Object.keys(this.entry[0].changes[0].value.statuses[0]).length === 0
         ) {