# WebViewer ReceivedMessage not working for Firebase alert in Thunkable

**URL:** <https://community.thunkable.com/t/webviewer-receivedmessage-not-working-for-firebase-alert-in-thunkable/4108297>\
**Category:** Web API's\
**Created:** [January 26, 2026, 10:32am UTC](https://community.thunkable.com/t/webviewer-receivedmessage-not-working-for-firebase-alert-in-thunkable/4108297 "2026-01-26T10:32:01Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![shahdnabil2348ygv3z4](https://avatars.discourse-cdn.com/v4/letter/s/ecd19e/32.png) [@shahdnabil2348ygv3z4](https://community.thunkable.com/u/shahdnabil2348ygv3z4)\
**Post date:** [January 26, 2026, 10:32am UTC](https://community.thunkable.com/t/webviewer-receivedmessage-not-working-for-firebase-alert-in-thunkable/4108297/1 "2026-01-26T10:32:01Z")

</div>

Hi Thunkable community,

I’m trying to make a **patient tracking app** using **WebViewer + Firebase**.  
Here’s what I want to do:

1. Show a **map in WebViewer** (Leaflet + Firebase Realtime DB).

2. Move a **marker** according to the patient’s location from Firebase.

3. Send an **alert to Thunkable app** (Notifier) when the patient goes out of a safe zone.

**What I have:**

- WebViewer shows the map and marker correctly.

- Marker moves and changes color inside WebViewer.

- Sound alarm works inside WebViewer.

**Problem:**

- `WebViewer.ReceivedMessage` in Thunkable **does not work** with the JSON message sent from my HTML.

- Some blocks (like JSON.parse) are missing in Thunkable.

**My question:**

- How can I **catch the message from WebViewer in Thunkable** if some blocks are missing?

- Is there a **full workaround** to trigger a Notifier alert inside Thunkable **without changing HTML**?

---

<div class="post-metadata">

**Author:** ![ioannis](https://sea1.discourse-cdn.com/flex015/user_avatar/community.thunkable.com/ioannis/32/146956_2.png) [@ioannis](https://community.thunkable.com/u/ioannis)\
**Post date:** [January 26, 2026, 10:33am UTC](https://community.thunkable.com/t/webviewer-receivedmessage-not-working-for-firebase-alert-in-thunkable/4108297/2 "2026-01-26T10:33:49Z")

</div>

Hi @shahdnabil2348ygv3z4  
We have changed only 1 thing, and it was a needed bugfix - when we post a message through the web viewer, previously, we were sending whatever type the user has chosen - e.g., if you send the number “1”, we’re sending 1 as a number. Now, we are stringifying everything, meaning that if you send “1”, it’ll be 1 as a string and not as a number. This means that, whoever is receiving or consuming the message, should handle it accordingly.

In the case of “1”, it’s “simple”. But if you decide to send a whole object (e.g., `{ name: 'John Doe', age: 20 }`, then this will be sent/received as a string, and the receiver must cast/parse it to an object and then they can use it as such

Could you please let me know if you have more questions?