sendMessage returns undefined

[iqrojp]

Issue Description

Client.sendMessage works, message sent but the function returns undefined

i even tested it with minimal code on fresh new node project

other thing i recall is i recently try to delete C:\Users\User\.cache while the whatsapp client is running, and i get a warning from windows that files inside it is in use, turns out it contains the chrome used by puppeteer.
but i stopped the whatsapp client, deleted the .cache folder and reinstalled it, but i dont know if thats the cause.

Reproduction Steps

1. call await Client.sendMessage()
2. log the value returned by sendMessage
3. it should be undefined

Code Sample

// minimal code tested on new project
...
import pkg from 'whatsapp-web.js';
const { Client, LocalAuth, MessageMedia, Buttons } = pkg;

...

// --- WA Client ---
const waClient = new Client({
  puppeteer: {
    args: ['--no-sandbox', '--disable-setuid-sandbox']
  },
  authStrategy: new LocalAuth({ dataPath: path.join(DATA_DIR, "sessions") }),
});

...

waClient.on('ready', async () => {
  console.log('WA client is READY');
  const sent = await waClient.sendMessage("*************@c.us", "Client ready"); // <--- here, 'sent' is undefined
  console.log('client ready message:', sent);
});

waClient.on("message_create", async (msg) => {
    console.log('Received', msg);
});

waClient.initialize();

User Setup

WhatsApp	Type
Account Type	Standard
Authentication Strategy	LocalAuth
WhatsApp Web Version	2.3000.1043612726
whatsapp-web.js Version	1.34.7

Environment	Version
Browser Type	chrome
Browser Version	win64-146.0.7680.31
Phone OS Version	android 10
Running OS Version	Windows 10
Node.js Version	22.19.0

Checklist

• I use the latest released version of whatsapp-web.js.
• I have searched existing issues and confirmed this is not a duplicate.
• I have verified this is a library issue, not a problem with my code.

[ShoyebOP]

I am also getting same issue-

cat tests/manual/temp/debug-test-+8801XXXXXXXXX-2026-07-22T15-14-07-489Z.ndjson
{"step":"client-init","data":{"status":"ok","initDurationMs":4069,"chromePath":"/usr/bin/chromium"},"timestamp":"2026-07-22T15:14:11.558Z"}
{"step":"send-attempt","data":{"chatId":"8801XXXXXXXXX@c.us","text":"Test message from capture-send"},"timestamp":"2026-07-22T15:14:11.558Z"}
{"step":"send-return","data":{"error":"Message returned undefined — unregistered number"},"timestamp":"2026-07-22T15:14:11.601Z"}

Even though in the morning I was getting ack=-1 error but the message was still getting sent in Whatsapp. And now it's not even sending it.

[sebabratakundu]

Facing the same issue. It wasn't there previously.

[gabriel-albqr]

estou enfrentando o mesmo problema,

reason=Cannot read properties of undefined (reading '_data')

[MohammadRHashem]

im also now experiencing Error: Reaction send error

[iqrojp]

I found the root cause and solution, but not sure which solution to use

whatsapp-web.js\src\util\Injected\Utils.js

    window.WWebJS.sendMessage = async (chat, content, options = {}) => {
...
        const newMsgKey = new (window.require('WAWebMsgKey'))({
            from: from,
            to: chat.id,
            id: newId,
            participant: participant,
            selfDir: 'out',
        });
        console.log('newMessageKey', newMsgKey); // <----- Root Cause #1
...

        const [msgPromise, sendMsgResultPromise] = window
            .require('WAWebSendMsgChatAction')
            .addAndSendMsgToChat(chat, message);
        await msgPromise;

        if (options.waitUntilMsgSent) await sendMsgResultPromise;

        return window
            .require('WAWebCollections')
            .Msg.get(newMsgKey._serialized); // <----- Root Cause #2
    };

Root cause:

1. _serialized is now $1 in Message:
   it seems they renamed _serialized to $1? (See code above).
   Output:

{
    "fromMe": true,
    "remote": "***********@lid",
    "id": "****************",
    "self": "out",
    "$1": "true_141880100663303@lid_3EB0DAE60958DAE18CED29_out" // <--- this should be '_serialized'
}

2. WAWebCollections can't find the sent message (See code above):
   window.require('WAWebCollections').Msg.get(newMsgKey._serialized); returned undefined.

My first attempt to fix the problem

At first i did not know about the _serialized renamed to $1, so my first guess is that window.require('WAWebCollections').Msg.get(newMsgKey._serialized) returns undefined because the message we sent has not been added to the WAWebCollections.Msg by the time the get() method was called. so my solution is to add a wait loop and a fallback to reconstruct the message manually.

whatsapp-web.js\src\util\Injected\Utils.js

    window.WWebJS.sendMessage = async (chat, content, options = {}) => {
...
        const [msgPromise, sendMsgResultPromise] = window
            .require('WAWebSendMsgChatAction')
            .addAndSendMsgToChat(chat, message);
        await msgPromise;

        if (options.waitUntilMsgSent) await sendMsgResultPromise;

-        return window
-           .require('WAWebCollections')
-            .Msg.get(newMsgKey._serialized); // <----- Root Cause #2
+      const msgKey = newMsgKey._serialized;
+      let sentMsg = window.require("WAWebCollections").Msg.get(msgKey);
+      if (!sentMsg) {
+      const MsgCollection = window.require("WAWebCollections").Msg;
+      for (let i = 0; i < 50; i++) {
+      await new Promise((resolve) => setTimeout(resolve, 100));
+      sentMsg = MsgCollection.get(msgKey);
+      if (sentMsg) break;
+  }
+}

+// Fallback: if still not found, construct model from the message object
+if (!sentMsg) {
+  sentMsg = new (window.require("WAWebCollections").Msg.modelClass)(message);
+}

+return sentMsg;
    };

miraculously this works, but im confused, _serialized doesnot exist in the message, so it just pops out of no where while i waited?

The Solution

This is the most obvious fix, since get() requires serialized message id, just use the $1 insted:

return window
            .require('WAWebCollections')
-            .Msg.get(newMsgKey._serialized);
+           .Msg.get(newMsgKey.$1);

and its fixed!

Solution 2?

this one im curious, addAndSendMsgToChat returns 2 Promises, and promise can return a value right? so i checked both promises return value, and it turns out msgPromise returns the sent message itself, so why is it just awaited an the values isnt used?
instead, it calls another module to search the message.

        const [msgPromise, sendMsgResultPromise] = window
            .require('WAWebSendMsgChatAction')
            .addAndSendMsgToChat(chat, message);
        await msgPromise; // <----- why?

why not just use the value?

...
const sentMsg = await msgPromise;
...
return sentMsg;
}

is there a particular reason to not just return the promise value?